-NRLF 


PRACTICAL  AVIATION 

including 

Construction  and  Operation 


By 
J.  ANDREW  WHITE 

Author  of  "Signal  Corps  Manual'' 

Director  of  Vocational  Training,  Marconi  Institute 


A    text  book    for  intensive  study   by  men  preparing    to    become    skilled 

mechanicians  and  aviators,  containing  all  the  knowledge  of  fundamentals 

required  prior  to  elementary  and  advanced  flying. 

Each  subject  is  presented  by  illustration  and    described    completely    for 
the  reader  without  turning  the   page. 

A  broad  treatment  of  subjects  never  before  contained  in  general  aeronautic 

text  books  is  included,  comprising  operation  and  care  of  aviation  engines, 

reconnaissance,  map  reading,  radio  and  its    uses,  machine   gunnery    and 

bombing  from  airplanes. 

Designed  particularly  for  individual  and  class  study  with  an  analysis  of 

important  factors  preceding  each    chapter  and  a  set  of  review  questions 

following   every  division. 


,  2J)6  ilJujtf  rations 


25  ELM   ST.n  rm^DhlklNEW  YORK 


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Copyright  1918 

BY 
WIRELESS  PRESS,  Inc. 


Foreword 

It  seems  to  be  generally  understood  that  the  real  value  of  a  textbook's 
foreword  is  measured  by  its  helpfulness  to  the  reader  in  explaining  how  the 
volume  may  be  studied  to  best  advantage.  Almost  without  exception,  what 
is  said  here  in  front  is  supplementary  and  of  a  postscript  nature,  for,  para- 
doxically, the  foreword  is  written  after  the  manuscript  has  been  completed. 

Seeking  to  play  the  game  according  to  the  rules,  I  am  forced  to  two 
conclusions:  First,  that  I  have  little  to  say  on  the  grouping  of  subjects 
and,  secondly,  that  the  typographical  arrangement  requires  some  explanation 
— perhaps  even  justification. 

I  will  dismiss  the  first  by  noting  merely  that  the  analysis,  in  skeleton 
form,  which  precedes  each  chapter  is  intended  as  a  guide,  aiding  dissection 
of  the  subject  into  easily  remembered  parts.  These  pages  are  in  many  ways 
comparable  to  the  instructor's  preliminary  talk  or  a  blackboard  outline  before 
the  class  takes  up  co-related  subjects  in  detail. 

To  explain,  or  justify,  if  you  choose,  the  typographical  appearance  of 
the  pages,  necessitates  striking  the  personal  note  for  a  minute.  The  idea 
had  its  origin  in  an  informal  talk  with  a  noncommissioned  officer  who  was 
among  the  students  of  an  aviation  ground  school  class  which  I  conducted 
at  the  outbreak  of  the  war.  By  accident,  his  notebook  came  to  my  hands. 
It  was  amazingly  comprehensive,  covering  by  diagram  and  data  an  entire 
series  of  lectures.  When  I  commended  the  student  for  its  compilation  he 
voiced  typically  youthful  impatience  with  its  limitations.  "I  try  to  jot 
down  each  important  thing  you  say,  Sir,"  he  complained,  "but  I  can't  seem 
to  get  them  verbatim.  The  diagrams  I  copy  from  the  blackboard;  that  is 
easy.  I  am  never  satisfied  with  my  notes,  though,  because  it's  so  hard  to 
distinguish  the  vital  thing  to  remember  as  you  go  along.  Now  if  I  could 
get  everything  word  for  word  and  devise  some  system  of  marking  so  I  could 
record  the  relative  emphasis  of  your  voice — well,  I'd  call  that  a  real  notebook." 

That  ended  the  episode.  But  in  it  was  born  the  idea  which  forms  the 
basis  of  this  book.  By  typographical  arrangement  I  have  presented  military 
aviation  as  it  has  been  taught  in  the  class  room.  The  diagrams  are  those 
which  have  proven  most  valuable  on  the  blackboard;  photographs  were 
chosen  from  among  those  projected  on  a  screen  by  balopticon.  Supporting 
text  explanation  of  the  illustrations  has  been  arranged  so  the  reader  is 
never  required  to  turn  the  page  to  apply  its  teachings — each  page  is  a  brief 
blackboard  talk  or  illustrated  lecture,  so  to  speak.  For  valuation  of  the 
importance  of  statements  I  have  used  relative  sizes  and  boldness  of  type. 

Thus  the  volume  appears  as  a  series  of  condensed  statements,  presented 
in  a  form  at  variance  with  usual  typographical  arrangements,  but,  I  hope, 
an  exceedingly  useful  one.  The  text  is  not  designed  for  those  merely  curious 
about  military  aviation,  nor  is  it  in  any  sense  a  treatise  on  aeronautical  engi- 

iii 


iv  Foreword 


neering.  The  entire  book  has  been  written  with  the  idea  of  possible  useful- 
ness to  student  aviators  who,  rising  to  a  military  emergency,  have  to  prepare 
in  the  shortest  possible  time. 

It  is  quite  true  that  flying  cannot  be  learned  by  reading  a  book.  But 
if  the  "reason  why"  is  made  known  by  the  printed  word,  the  process  of 
mastering  actual  airplane  manipulation  is  made  shorter  and  safer  for  the 
aviation  candidate.  And  in  acquiring  this  understanding  of  an  art  which 
is  undergoing  constant  change,  best  results  are  attained  by  concentrating 
on  fundamentals.  For,  once  a  sound  knowledge  of  aerodynamic  principles 
and  elements  of  design  is  acquired,  the  constant  technical  changes  in  aircraft 
and  their  employment — even  those  advances  which  at  first  glance  appear 
revolutionary — may  be  easily  understood. 

That  is  why,  in  the  pages  following,  no  particular  type  of  airplane  con- 
struction has  been  emphasized,  no  special  motor  featured.  Where  a  method 
of  control  or  use  of  an  airplane  has  been  explained,  the  endeavor  has  been 
to  select  the  practice  which  presents  the  basic  principle  upon  which 
modifications  rest. 

A  Review  Quiz  follows  each  chapter.  The  questions  are  purposely  not 
exhaustive.  Each  one  is  designed,  however,  to  start  a  train  of  thought  in 
the  mind  of  the  reader  which  will  encourage  him  to  turn  back  and  dig  into 
parts  of  the  text  which  he  may  have  skipped  over  too  lightly. 

,  It  may  also  be  noted  that  the  decorative  style  of  writing  has  been 
diligently  repressed.  More  than  once  in  preparing  the  manuscript  the 
temptation  arose  to  illustrate  a  point  by  a  humorous  or  dramatic  anecdote; 
but  in  all  instances  it  was  regretfully  set  aside.  The  method  of  presentation 
demanded  concise  statement,  else  the  reading  matter  essential  to  under- 
standing of  the  illustrations  would  have  carried  over  the  page. 

Widely  varied  aspects  of  flying  are  treated  in  the  fifteen  chapters;  in 
many  of  these  the  consensus  of  best  obtainable  opinion  has  ruled  in  the 
absence  of  finally  established  practice.  In  fact,  all  through  the  text  the 
opinion  of  General  Sir  David  Henderson  has  been  borne  in  mind,  that: 
"There  are  no  experts  in  military  aeronautics.  There  are  experts  in  the 
various  branches:  in  flying,  in  scientific  research,  in  the  design  and  con- 
struction of  airplanes  and  engines,  in  military  organization  and  tactics." 
In  consequence  of  which  many  practical  men  have  been  consulted  in  the 
endeavor  to  place  into  this  volume  the  best  thought  of  specialists  in  each 
subject.  Since  aviation  still  remains  in  a  transitory  stage  from  an  art  to  a 
science,  further  comment  from  readers  will  be  cordially  welcomed  and  care- 
fully weighed  with  a  view  to  improving  future  editions. 

In  conclusion,  I  should  like  to  acknowledge  the  assistance  of  Mr.  William 
J.  Hernan  and  Lieut.  Marius  Mignot  in  supplying  for  the  terms  defined  in 
the  nomenclature  French  equivalents  and  their  phonetic  pronunciation.  With 
generous  thanks  also  to  the  many  others  who  criticized  the  book  in  manu- 
script form,  I  send  the  volume  on  its  journey  to  make  its  bid  for  approval  on 
the  sincerity  with  which  it  was  written — solely,  simply  and  finally  for 
military  aviators,  to  whom  it  is  dedicated  with  the  hope  that  it  will  be  useful 
in  their  preliminary  and  supplemental  study  to  the  ultimate  end  of 
becoming  qualified  airmen. 

J.   ANDREW  WHITE. 


Contents 

CHAPTER  I 

Theory  and  Principles  of  Flight 1 

-Types  of  Airplanes— Helicopter  and  Ornithopter — Pusher  and  Tractor — 
Monoplane,  Biplane  and  Triplane — Axes  of  Rotation — Principle  of  Flight — 
Lift  by  Air  Pressure  and  Suction — Lift  and  Drift — Lift-Drift  Ratio — Angle 
of  Incidence — Camber — Aspect  Ratio — Stagger. 

CHAPTER  II 

Elements  of  Airplane  Design 13 

Factors  of  Superiority,  in  Design — Climbing  Rate — Greatest  Speed — Hori- 
zontal Equivalent— Design  for  Maximum  Climb — Design  for  Maximum 
Velocity — Angles  of  Incidence  in  Flight — Minimum — Optimum — Best 
Climb — Maximum. 

CHAPTER  III 

Flight  Stability  and  Control 21 

Airplane  Equilibrium — Stability — Longitudinal  Stability — Lateral  Stabil- 
ity— Directional  Stability — Center  of  Gravity — Washout  and  Washin — Aile- 
rons— Banking — Controls^-Wheel  and  Column — Joystick. 

CHAPTER  IV 

Materials,  Stresses  and  Strains 33 

Action  on  Materials — Stress — Strain — Factor  of  Safety — Stress  and  Strain 
Forces — Strength  of  Wood  Under  Stress — Wood  for  Airplanes — Wing 
Covering — Fabric — Dope— Metal  Fittings  and  Wire. 

CHAPTER  V 

ng  the   Airplane 41 

Erection  and  Assembly — Landing  Gear — Horizontal  Stabilizer — Vertical 
Stabilizer — Rudder — Elevators — Assembly  of  Lifting  Surfaces — Alignment — 
Over-all  Adjustments — Control  Cables  and  Wires— Effect  of  Alignment  Er- 
rors—Flight Defects. 

CHAPTER  VI 

Fundamentals  of  Motive  Power 51 

The  Propeller — Balance — Care — The  Gasoline  Engine  Cylinder — Combus- 
tion Chamber — Piston — Connecting  Rod — Crank  Shaft — Revolution — The 
Four-Cycle  Principle — Multiple  Cylinder  Engines — 4-Cylinder  Operation — 
6-Cylinder  Operation. 


CHAPTER  VII 

Pistons,  Valves  and  Carburetors 63 

The  Piston* — Crank  Shaft — Crank  Case — Valves  and  Valve  Mechanism — 
Camshaft — Cams — Valve  Operating  Mechanism — Valve  Clearance — Car- 
buretion — Principle  of  the  Carburetor — Construction. 

CHAPTER  VIII 

Ignition,  Cooling  and  Lubrication  of  Engines 73 

Ignition— Magneto — Distributor — Condenser— Circuit  Breaker— Spark  Plug 
— Cooling — Water  Cooling — Air  Cooling — Lubrication  —  Splash  —  Force 
Feed. 


CHAPTER  IX 

Types  of  Motors,  Operation  and  Care  of  Engines 79 

Bore  and  Stroke  Ratio— V-Type  Motors — 8-Cylinder — 12-Cylinder— The 
Liberty  Motor— Rotary  Engines — The  Gnome  Engine — Starting  the  Engine 
— Fuel  Conservation  in  Flight — Care  of  Engines — General  Rules — The 
Trouble  Chart. 

CHAPTER  X 

Instruments  and  Equipment  for  Flight 95 

Aviator's  Equipment — Clothing — Safety  Belt — Airplane  Instruments— Scope 
and  Usefulness — Cockpit  Arrangement — Gauges — Compass — Barometer  or 
Altimeter — Tachometer — Angle  of  Incidence  Indicator — Inclinometer — 
Drift  Meter — Air  Speed  Meter — Banking  Indicator. 

CHAPTER  XI 

First  Flights  and  Cross-Country  Flights 103 

Instruction  in  Flying — First  Flights— Right  of  Way— Landing — Use  of  the 
Compass — Compass  Error — Adjusting  the  Compass — Laying  Off  a  Course — 
Data  Required — Radius  of  Action — Some  Flight  Considerations — Lost 
Bearings — Landmarks — Time  Checking — Forced  Landings — Re-Starting — 
Map  Reading — The  Flying  Crew — The  Repair  Crew. 

CHAPTER  XII 

Aerobatics  and  Night  Flights 127 

Advanced  Flying — Spiral — Nose  Dive — Spinning  Nose  Dive — Aerobatics — 
Loop  the  Loop — Vertical  Bank — Zooming — Roll  Over — Spiral  Loop — Im- 
melman  Turn — Night  Flying — Preliminary  Instruction — Landing  at  Night. 

CHAPTER  XIII 

Meteorology  for  the  Airman 137 

Characteristics  of  the  Air — Atmospheric  Pressure — Pressure  Areas — Cy- 
clone Area — Anti-cyclone  Area — Line  Squalls — Beaufort  Scale — Wind  Con- 
ditions Which  Affect  Aviation — Aerial  Fountain — Aerial  Cataract — Wind 
Layers — Wind  Gusts  and  Eddies — Clouds  and  Their.  Significance. 

CHAPTER  XIV 

Aerial  Gunnery  and  Combat — Bombs  and  Bombing 147 

Combat  Airplanes — Factors  of  Success  in  Air  Combat — The  Lewis  Machine 
Gun — Accuracy  and  Volume  of  Fire — Ammunition  and  Fire  Correction — 
Gun   Mountings  and   Fire   Radius — Fighting  in  the   Air — Aerial   Tactics — 
Contact  Patrol — Anti-Aircraft  Fire — Bombing  Air  Raids — Types  of  Bombs 
— Bomb  Dropping — Use  of  the  Range   Finder. 

CHAPTER  XV 

Reconnaissance  and  Fire   Spotting 171 

Reconnaissance  by  Airplane — Orders  for  Reconnaissance  Flights — Tactical 
Reconnaissance — Estimates  of  Enemy  Strength — Strategical  Reconnais- 
sance— Reports  of  Flights — Instruction  in  Code  Telegraphing — Proper  Grip 
on  the  Key — Sending — Receiving — Directing  Artillery  Fire — Types  of 
Shells — Ranging — Observer's  Map  and  Code  Signals — Signals  from  the 
Ground — Radio  (Wireless)  Telegraphy — Airplane  Radio  Apparatus — Aerial 
Photography. 

APPENDIX 

Nomenclature  of  Aeronautical  Terms — French  Equivalents — Phonetic  Pro- 
nunciation— Metric  Conversion  Tables — Rules  for  Mensuration. 

vi 


viii  Practical    Aviation 


CHAPTER  ANALYSIS 

The  Theory  and  Principles  of  Flight 

TYPES  OF  AIRPLANES: 

(a)  Helicopter. 

(b)  Ornithopter. 

(c)  Tractor. 

(d)  Pusher. 

(e)  Monoplane. 

(f)  Biplane. 

(g)  Triplane. 

AXES  OF  ROTATION: 

(a)  Pitching. 

(b)  Yawing. 

(c)  Banking. 

THE  PRINCIPLE  OF  FLIGHT: 

(a)  Air  Pressure. 

(b)  The  Aerofoil. 

(c)  Camber. 

(d)  Chord  and  Span. 

(e)  Angle  of  Incidence. 

LIFT   BY   AIR   PRESSURE   AND  SUCTION: 

(a)  Lift. 

(b)  Drift. 

(c)  Lift-Drift  Ratio. 

(d)  Velocity. 

(e)  Flow  of  Air. 

(f)  Aspect  Ratio. 

(g)  Stagger. 


CHAPTER  I 

The  Theory  and  Principles  of  Flight 

It  is  natural  for  the  student  aviator  to  be  more  or  less  impatient  with 
the  technical  side  of  aviation.  He  is  anxious  to  fly  immediately,  and  rather 
disposed  toward  acquiring  his  knowledge  of  fundamentals  at  some  later  date. 
This  mental  attitude  must  be  overcome;  many  tragic  occurrences  have  had 
their  origin  in  impatience. 

The  military  aviator's  success  largely  depends  upon  his  acquaintance 
with  the  essential  features  of  airplane  design — why  the  machine  flies  and 
what  makes  it  stable.  Safety  in  maneuvering  in  air  battles  and  flying  effi- 
ciency is  based  on  knowledge  of  the  theory  of  dynamic  flight  and  the  limita- 
tions of  his  machine.  The  noticeably  exaggerated  movements  of  controls  by 
students  in  first  flights,  too,  are  due  not  alone  to  nervousness,  but  to  igno- 
rance of  the  sensitiveness  of  the  control  surfaces,  all  of  which  function  in 
accordance  with  flight  laws. 

Theoretical  knowledge  is  necessary.  That  it  can  be  satisfactorily  ac- 
quired by  textbook  study  has  been  demonstrated  and  it  is  expected  that  the 
reader  will  begin  the  study  of  these  pages  with  a  firm  conviction  that  the 
prospective  aviator  must  be  thoroughly  grounded  in  fundamentals. 

Military  airplanes  will  of  course  be  given  first  consideration.  Some 
aeronautical  generalities  are  necessary,  however,  in  dealing  with  design  and 
construction,  but  these  will  be  treated  briefly. 

The  airplane  is  but  one  form  of  flying  machine.  Leaving  balloons  of 
various  types  entirely  outside  the  question,  there  still  remain  three  types  of 
heavier-than-air  machines.  While  study  will  be  concentrated  on  the  airplane, 
passing  reference  should  be  made  to  the  other  two  types  before  proceeding. 
These  are : 

The  Helicopter — a  machine  which  employs  the  principle  of  direct  lift  by 
means  of  an  air  screw  propeller  operating  on  a  vertical  axis.  This  is  not  a 
practical  type  of  flying  machine  and  little  has  been  done  with  it. 

The  Ornithopter — a  machine  which  derives  its  name  from  the  bird,  its 
principle  being  the  creation  of  flapping  wings  given  a  reciprocal  motion 
somewhat  similar  to  rowing,  the  forward  push  intended  to  exactly  counter- 
feit that  of  the  bird's  wings.  These  machines  are  not  yet  successful. 

The  reader  may  be  fascinated  by  the  possibilities  of  research  into  the 
field  represented  by  this  latter  type,  but  considering  the  present  efficiency  of 
the  airplane,  it  is  safe  to  assume  that  time  will  be  better  spent  in  utilizing  its 
man-discovered  principles  of  flight,  rather  than  in  following  a  new  line  of 
thought  on  the  assumption  that  Nature  never  makes  a  mistake  and  the  bird 
is  therefore  the  best  model. 

It  must  be  remembered  that  flying  is  but  an  incident  in  the  life  of  a  bird, 
just  as  walking  is  to  a  man.  The  famous  aviator  Santos-Dumont  drew  a 

1 


Frc-cti«-,al    Aviation 


An  airplane  of  the  "tractor"  type,  so  called  because  the  propeller  is  attached  to  the  front, 

pulling  the  machine  through  the  air 


parallel  which  disclosed  the  folly  of  blindly  following  Nature,  when  he 
pointed  out  that  such  a  procedure  would  have  resulted  in  locomotives  being 
built  with  huge  iron  legs  and  steamships  with  the  flapping  fins  and  lashing 
tail  of  the  whale.  Sir  Hiram  Maxim  further  blasted  the  bird-flight  theory 
by  noting  that  "in  order  to  build  a  flying  machine  with  flapping  wings,  to 
exactly  imitate  birds,  a  very  complicated  system  of  levers,  cams,  cranks,  etc., 
would  have  to  be  employed,  and  these  of  themselves  would  weigh  more  than 
the  wings  would  lift." 

Without  further  comment,  therefore,  the  study  will  be  confined  to  the 
airplane,  the  most  successful  type  of  aircraft  and  the  best  developed  means  of 
navigating  the  air. 

The  airplane  is  sustained  by  the  upward  push  of  the  air  flowing  past  it ; 
it  therefore  is  composed  of  (a)  lifting  surfaces,  (b)  power  for  propulsion. 

Propulsion  through  the  air  is  effected  by  a  propeller,  identical  in  prin- 
ciple though  not  in  appearance,  to  the  screw  on  a  boat.  An  engine  drives 
this  propeller  at  the  required  velocity.  The  propulsion  produced  by  the  pro- 
peller is  called  the  thrust. 

When  the  propeller  is  attached  to  the  front,  pulling  the  machine  through 
the  air,  the  airplane  is  called  a  tractor. 

If  the  propeller  is  back  of  the  wings,  or  main  lifting  surfaces,  the  airplane 
is  called  a  pusher. 

The  tractor  type,  with  a  single  propeller,  is  generally  acknowledged 
the  most  efficient  all-round  machine,  although  pushers  with  two  air  screws 
have  distinct  values  in  gun-carrying  machines. 

An  airplane  with  two  wings,  one  above  the  other,  is  known  as  a  biplane. 

One  with  three  wings  is  called  a  triplane. 


Types    of    Airplanes 


A  "pusher"  biplane  with  the  propeller  back  of  the  wings  or  main  lifting  surfaces  and  the 

pilot's    seat   directly    in    front 


The  single  wing  type,  with  one  lifting  surface,  is  called  a  monoplane. 

The  tractor  biplane  is  the  type  which  is  more  nearly  standardized  and  will 
be  principally  considered  here. 


The  main  lifting  surfaces  are  planes,  or  "wings,"  which  present  their 
widest  dimension  across  the  line  of  flight  and  create  the  air  compression  on 
their  surfaces  which  produces  flight. 

The  body  to  which  these  planes  are  attached  is  known  as  the  fuselage, 
the  engine  and  seats  mounted  in  it  being  enclosed  to  lessen  the  resistance  of 
the  wind. 

In  pusher  types  the  body  is  called  the  nacelle. 

Since  the  airplane  "sails"  through  the  free  air,  it  has  three  axes  of  rota- 
tion. 

(1)  It  may  ascend  or  descend.     This  is  known  as  pitching,  and  is  con- 
trolled by  depressing  or  elevating  an  elevator  by  means  of  suitable  controls. 

(2)  It  may  change  its  direction  of  travel,  or  steer  to  right  and  left. 
This  is  called  yawing,  and  is  made  possible  by  the  operation  of  the  rudder. 

(3)  •  It  may  tip  over  to  either  side,  a  movement  termed  banking  or  roll- 
ing.    This  lateral  motion  is  offset  by  three  means  of  control  which  give  a  dif- 
ference in  angle  to  the  two  sides  of  the  wing  surface,  causing  one  side  to  lift 
more   than   the   other.     The   controls   are:      (a)    ailerons,    small   planes   set   at 
each   side,   between   and   independent   of  the   main   lifting   surfaces;    (b)    wing 
flaps,  also  called  ailerons,  which  are  hinged  portions  of  the  main  planes;   (c) 
warping,  or  twisting  the  main  lifting  surfaces  to  simultaneously  lessen  and  in- 
crease the  angle  of  inclination  to  the  wind  a's  required  on  both  sides. 


Practical    Aviation 


An  aerofoil 
or  surface 


Figure  1 — A  lifting  surface 


THE  PRINCIPLE  OF  FLIGHT 

The  upward  air  pressure  against  its  main  wing  surfaces  enables  the 
airplane  to  fly,  when  these  wing  surfaces,  or  planes,  are  set  at  an  angle 
inclined  from  the  direction  of  motion,  the  pressure  being  supplied  by  the 
speed  at  which  the  planes  are  driven  by  the  propeller. 

AIR — Air  is  attracted  by  the  mass  of  earth,  or  the  gravity  force,  and  therefore 
has  weight.  A  cubic  foot  of  dry  air,  at  sea  level  and  32  degrees  Fahrenheit  tempera- 
ture, weighs  0.0807  Ib.  Its  density  decreases  with  altitude,  until  at  a  mile  above  sea 
level  it  weighs  0.0619  Ib.,  and  at  five  miles,  0.0309  Ib.  per  cubic  foot. 

Air  also  has  motion,  which  must  be  taken  into  consideration  by  the  aviator,  and 
resistance,  due  to  density  and  intensity  of  motion,  or  wind.  Air  resistance  comprises: 

Inertia — Its  tendency  to  remain  at  rest,  if  still;  in  motion,  if  moving. 

Elasticity — Its  tendency  to  reoccupy  its  normal  amount  of  space  after  being  dis- 
turbed. 

Viscosity — The  tendency  of  particles  of  air  to  resist  separation. 

Inertia  gives  the  propeller  its  "hold"  in  the  air;  elasticity,  when  air  is  compressed 
under  the  surface  of  the  plane,  aids  the  lift;  viscosity  creates  friction,  which  is  min- 
imized by  using  polished  surfaces  and  stream-lining  airplane  parts. 

THE  SURFACE 

A  wing  surface  is  meant  by  this  expression  (see  Figure  1).  It  has  a 
strictly  aeronautical  designation,  viz.: 

THE  AEROFOIL 

This  term  is  seldom  used  by  aviators,  but  is  commonly  employed  by 
aeronautical  engineers  to  differentiate  between  an  ordinary  surface  and  one 
inclined  at  an  angle  to  the  direction  of  motion,  having  thickness,  and  curved 
to  secure  a  reaction  from  the  air  for  lifting. 

CAMBER 


This  is  the  term  which   designates   the  curvature   of  the   surface,   or 
aerofoil. 


Definitions  of  Wing  Terms 


Figure  2 — The  chord  and  span  of  a  wing  surface 


THE  CHORD 


This  is  the  dimension  of  an  imaginary  straight  line  from  the  front  edge 
of  the  aerofoil,  or  surface,  to  the  rear  edge,  as  shown  by  A — JB,  in  Figure  2. 

The  front  edge  of  the  wing  is  known  as  the  leading  edge,  and  the  rear 
as  the  trailing  edge. 

SPAN 

This  is  the  dimension  of  the  surface  across  the  direction  of  motion,  indi- 
cated by  A — C,  in  Figure  2. 

THE  ANGLE  OF  INCIDENCE 

This  is  the  angle  of  inclination  of  the  chord  to  the  air  stream. 

In  practice  this  is  the  angle  of  inclination  of  the  chord  to  the  line  of  the 
propeller  thrust.  If  the  leading  edge  of  a  surface  is  above  the  trailing  edge 
when  driven  through  the  air,  the  angle  of  incidence  is  positive.  A  surface 
with  the  trailing  edge  presented  above  the  leading  edge,  or  negatively  to 
the  air  flow,  would  bring  the  air  pressure  to  the  top  of  the  surface  and  con- 
stitute a  negative  angle, 


LIFT  BY  AIR  PRESSURE  AND  SUCTION 

The  airplane  wing  having  been  considered  as  a  surface,  its  action  upon 
the  air  may  be  described. 

Air,  or  the  atmosphere,  has  characteristics  similar  to  water,  the  atmos- 
phere being  an  ocean  of  definite  extent  and  pressure  at  different  altitudes, 
and  flowing  past  an  object  either  in  stream  lines,  or  in  broken  up  eddies  due 
to  disturbances  in  its  flow. 


Practical    Aviation 


Undisturbed  oir 


Partial  vacuum  aiding  lift 


Air  compressed  for  lift 
-* D/recf/on  of  mot  ion — OSK 

Figure  3 — Action  of  air  on  the  aerofoil 


The  nature  of  the  air  pressure  when  encountering  the  aerofoil  is  shown 
in  the  drawing,  Figure  3. 

The  under  face  of  the  airplane  wing  compresses  the  air,  resulting  in  a 
positive  force. 

At  the  same  time  a  suction  is  caused  by  the  air  flowing  past  the  upper 
face,  causing  a  partial  vacuum,  tending  to  draw  the  surface  upward. 

The  value  of  this  suction  is  about  three-fifths  of  the  total  pounds  force 
of  the  air's  action  on  the  aerofoil.  The  factors  of  this  air  reaction  are: 

(a)  The  mass  of  the  air. 

(b)  The  velocity^ofjthe_aerpfoil. 

The  reaction  increase  is  as  the  square  of  the  velocity. 
The~air  lrea~ction  has  two^valuesl 

LIFT — opposed  to  gravity,  or  the  airplane's  weight. 
DRIFT — opposed  to  the  thrust  of  the  propeller. 

The  lift  is  opposed  by  the  drift,  which  must  be  overcome  by  the  thrust 
supplying  velocity  great  enough  to  produce  an  air  reaction  sufficient  to  pro- 
duce flight. 

Drift  is  of  three  kinds:  (a)  active  drift,  produced  by  the  velocity  of  the  lifting 
surfaces;  (b)  passive  drift,  the  resistance  of  other  parts  of  the  airplane,  such  as  struts, 
wires,  tank,  fuselage,  hood,  etc.;  (c)  skin  friction,  or  the  air  resistance  on  roughness 
of  surface. 

LIFT  AND  DRIFT 

It  has  been  shown  how  the  air  pressure  is  created  on  a  surface  inclined 
at  a  positive  angle  to  the  direction  of  motion,  and  that  this  pressure  exerts 
a  lifting  force. 

The  air  pressure  is  inclined  upward  and  to  the  rear  of  the  direction  of 
motion  in  a  ratio  equal  to  the  variance  of  the  angle  of  incidence  of  the  wing 
plane. 

The  vertical  action  of  the  air  pressure  is  a  force  capable  of  lifting  weight 
but  its  horizontal  component  of  air  pressure  represents  resistance  to  motion. 

Thus,  while 

LIFT  is  a  vertical  air  pressure. 

DRIFT,  its  horizontal  component,  is  resistance. 


Lift-Drift    Ratio 


Figure  4 


Direction  of    

motion 

Figure  5 
LIFT-DRIFT  RATIO 


-  Drlff 


\\\\\\vw\ 

Figure  6 


Flight  \§  maintained  by  the  proportion  of  lift  to  drift  being  sufficiently 
great  to  overcome  the  force  of  drift.  The  characteristics  of  the  wing  surface 
are  designed  for  the  greatest  lift  with  the  smallest  consequent  drift,  so  that 
minimum  power  supplies  maximum  capacity  for  load  carrying. 

The  factors  to  be  considered  in  determining  lift-drift  ratio  are  velocity, 
angle  of  incidence,  camber  and  aspect  ratio. 

VELOCITY 

Drift  increases  to  lift  proportionately  with  increase  of  velocity. 

Active  drift,  formed  by  the  wing  surfaces,  is  a  component  part  of  the 
air  reaction  which  creates  the  lift,  and  therefore  increases  as  the  square  of 
the  velocity.  At  all  speeds  the  efficiency  of  the  airplane  would  remain  the 
same,  but  for  the 

Passive  drift,  or  the  resistance  of  the  airplane  parts  other  than  the  lifting 
surfaces,  which  also  increases  as  the  square  of  the  velocity,  yet  adds  nothing 
to  the  lift.  Thus  by  adding  its  resistance  to  the  active  lift,  it  prevents  the 
airplane's  ratio  of  lift  to  drift  from  increasing  proportionately  with  the  in- 
crease of  the  thrust.  In  other  words,  the  efficiency  of  the  airplane  would  not 
decrease  with  added  velocity,  if  it  were  not  for  the  passive  drift.  This 
factor  prevents,  so  to  speak,  doubling  the  speed  or  lift  by  doubling  the  thrust. 

To  diminish  the  passive  drift  all  parts  of  the  airplane  are  given  stream 
lines,  or  a  form  offering  least  resistance  as  they  pass  through  the  air. 

Head  resistance  is  a  term  formerly  employed  to  described  passive  drift.  It  has 
been  largely  discarded,  however,  for  its  inaccuracy  of  description  of  the  effect  of  the 
action  of  parts  in  air  reaction.  Passive  drift  is  due  more  to  the  action  on  the  rarefied 
area  behind  the  object  than  to  the  head  or  forward  part  of  hood,  struts,  wires,  etc. 

FLOW  OF  AIR 

Figures  4,  5,  6  illustrate  the  flow  of  air  around  three  objects  of  varying 
form. 

In  Figure  4  the  rarefied  area,  or  drift,  is  represented  by  D — D,  and  is  of 
marked  extent. 

In  Figue  5,  this  area,  indicated  by  the  same  symbol,  has  decreased,  the 
air  flowing  closer  to  the  spherical  body. 

Figure  6  shows  the  rarefied  area  still  further  diminished,  the  shape  of  the 
body  being  conducive  to  closer  air  flow. 

These  three  figures  illustrate  the  importance  of  stream-lining  parts  on 
the  line  of  flight. 

As  the  head  resistance  is  increased  by  the  rarefied  area  in  the  rear  of 
the  object,  the  thrust  required  increases  proportionately. 

The  action  of  air  on  objects  of  different  shapes  and  propelled  at  varying  veloc- 
ities is  determined  by  visualizing  the  air  in  laboratory  research  with  wind  tunnels. 


Practical    Aviation 


ANGLE  OF  INCIDENCE 

This  is  the  angle  of  inclination  of  the  chord  to  the  air  stream.  Its  effi- 
ciency varies  and  is  determined  by  what  is  desired  in  thrust,  weight-carrying 
capacity,  and  ratio  of  climb  to  velocity. 

It  may  be  accepted  as  a  general  premise  that  the  greater  the  velocity 
the  smaller  should  be  the  angle  of  incidence,  so  that  the  rarefied  area  may 
be  kept  to  stream-lines  and  the  eddies  of  air  reduced  to  a  minimum.  These 
eddies  represent  drift,  since  they  have  no  lift,  and  when  produced  by  too 
great  an  angle  of  incidence,  the  power  required  to  produce  them  is  wasted, 
with  consequent  loss  in  efficiency  of  the  airplane. 

>. 

Wind  tunnel  research  largely  determines  the  best  angles  of  incidence. 


CAMBER 

The  purpose  of  the  camber,  or  curve,  in  a  lifting  surface  is  to  decrease 
the  active  drift,  horizontal  component  of  the  lift. 

Camber  of  lower  face — The  horizontal  air  reaction  from  a  flat  surface 
would  be  considerable  and  increase  the  drift.  Curving  the  wing  surface 
compresses  and  accelerates  the  air  from  the  leading  edge  to  the  trailing 
edge.  If  this  air  action  is  not  uniform  the  drift  will  be  increased.' 

With  a  fixed  upper  face,  an  increase  in  the  camber  of  the  lower  face  does  not 
greatly  vary  the  relation  of  lift  to  drift,  but  lift  increases  with  camber  increase.  Most 
of  the  lift  is  furnished  by  the  upper  face,  however,  and  the  camber  increase  of  the 
lower  does  not  produce  sufficient  effect  on  the  upper  to  compensate  for  the  lessened 
depth  of  spar  allowed  when  a  rather  flat  surface  is  used.  Decreased  depth  of  spar  per- 
mits a  weight  reduction  in  the  framework  of  the  wing  without  sacrifice  of  strength. 
It  is  for  this  reason  that  lessened  camber  for  the  under  side  is  allowed. 

Camber  of  upper  face — The  top  surface  is  curved  to  produce  the  least 
possible  eddies  of  air  resistance  behind  the  trailing  edges,  the  rarefied  area 
produced  being  given  the  best  obtainable  stream  line  to  lessen  the  drift  in 
the  lift-drift  ratio. 

Velocity,  angle  of  incidence  and  thickness  of  aerofoil,  or  surface,  deter- 
mines the  camber  of  the  upper  face.  In  general,  the  camber  and  angle  of 
incidence  should  decrease  proportionately  with  velocity  increase. 

On  an  aerofoil  with  a  Hat  under  face  the  maximum  lift  increases  with  the  upper 
face  cambered  up  to  1/15,  beyond  which  it  decreases.  Improvement  of  the  lift-drift 
ratio  is  steady  up  to  1/20  camber,  thereafter  showing  decrease  in  value  with  deeper 
cambers. 

With  the  under  face  cambered  the  increase  of  upper  face  camber  above  1/15  shows 
little  variation  in  lift,  but  steady  increase  of  drift. 


Aspect    Ratio 


J6'- 


•—  ? 

^=n? 

L 

a 

Q 

Figure  7 — High  aspect  ratio 


Figure  8 — Low  aspect  ratio 


ASPECT  RATIO 

The  proportion  of  span  to  chord  is  the  aspect  ratio.  The  total  span 
divided  by  the  chord  of  the  wings  is  the  "aspect"  of  an  airplane. 

In  Figure  7  the  span  is  36  feet,  the  chord  is  6  feet,  the  aspect  ratio  is 
therefore  6  to  1. 

Figure  8  shows  a  span  of  30  feet  and  a  chord  of  10  feet,  an  aspect  of  3. 

At  a  given  velocity  and  given  wing  area,  the  reaction  increases  with 
increase  in  aspect  ratio.  The  reason  for  this  is  that  a  greater  mass  of  air  is 
engaged  with  a  wider  span,  the  reaction  of  air  being  partly  the  result  of  the 
mass  of  air  engaged. 

An  average  aspect  for  an  airplane  is  6,  but  in  deep  cambered  planes  an  aspect  of 
9  is  considered  practicable  by  designers. 

The  usual  limits  are  2  to  8.     High  speed  airplanes  of  the  pursuit  type  seldom  ex- 
ceed an   aspect  ratio  of  5. 

In  a  general  way  it  may  be  said  that  the  higher  the  aspect  ratio,  the 
better  is  the  lift-drift  ratio.  But  with  decrease  of  chord  the  deepening  of  the 
camber  requires  added  thickness  of  aerofoil,  or  surface,  and  in  practice  the 
reduction  of  chord  required  for  an  extremely  high  aspect  ratio  makes  pro- 
hibitive the  use  of  the  thickness  of  surface  which  would  give  the  best  camber. 


The  "spill"  of  the  air  from  under  the  tips  of  the  wings  also  has  some 
bearing  on  aspect  ratio,  since  with  wings  of  small  span  this  loss  in  lift  is 
material,  whereas  in  wings  of  wide  span  the  percentage  is  small  and  the 
loss  inconsequent.  It  is  because  of  the  slight  lift  gained  in  proportion  to 
the  air  disturbance  that  wing  tips  are  rounded  off  in  many  airplanes. 


10 


Practical    Aviation 


Line  of  the  vertical 


Figure  9 — The  upper  plane  placed  in  advance  of  the  lower,  or  staggered 


STAGGER 


When  the  top  surface  of  a  biplane  is  placed  in  advance  of  the  vertical 
with  relation  to  the  lower  wing  surface,  the  term  stagger  is  used. 


See  Figure  9. 


By  staggering  the  upper  plane  ahead  of  the  lower  plane  it  is  removed 
from  the  area  of  action  of  the  lower  aerofoil  and  engages  undisturbed  air. 

Without  stagger,  the  confusion  of  air  reaction  could  be  obviated  by 
increasing  the  gap  between  upper  and  lower  planes  a  dimension  equal  to  ll/2 
times  the  chord.  But  the  length  of  struts  and  wires  required  for  this  open- 
ing increases  the  drift,  making  it  impracticable  to  have  a  gap  much  greater 
than  the  chord. 


Minor  considerations  of  construction  and  balance,  and  visibility  for  pilot 
and  observer,  govern  the  proportion  of  stagger,  although,  theoretically,  the 
upper  plane  should  be  advanced  a  distance  about  equal  to  30  per  cent,  of  the 
chord,  small  variations  being  further  governed  by  velocity  and  angle  of 
incidence. 


Practical    Aviation  1 1 


REVIEW  QUIZ 

Theory  and  Principles  of  Flight 

1.  Describe  three  types  of  heavier-than-air  machines  and  state  their 

practicability. 

2.  Define  three  main  divisions  in  the  uses  of  military  airplanes  which 

govern  types. 

3.  State  the  fundamental  principle  which  makes  flight  possible. 

4.  What  is  meant  by  the  inertia  of  air? 

5.  What  is  the  aeronautical  term  for  a  wing  surface,  and  how  does  it 

differ  from  an  ordinary  surface? 

6.  Define  camber. 

7.  How  is  the  dimension  of  the  chord  of  an  airplane  taken?    The  span? 

8.  Give  a  full  definition  of  the  angle  of  incidence. 

9.  In  what  way  does  atmosphere  resemble  water? 

10.  What  is  the  action  on  air  when  it  encounters  the  under  face  of  the 

aerofoil? 

11.  State  what  proportion  of  lift  is  represented  in  the  partial  vacuum 

above  the  upper  face. 

12.  What  are  the  two  values  of  air  reaction? 

13.  Define  three  kinds  of  drift. 

14.  What  is  lift-drift  ratio  and  how  r.re  the  characteristics  of  the  wing 

surface  governed  by  it? 

15.  State  the  four  factors  to  be  considered  in  determining  lift-drift  ratio. 

16.  Define  two  kinds  of  drift  created  by  velocity  and  state  how  these 

affect  flight  efficiency. 

17.  Show  by  a  simple  diagram  why  head  resistance  requires  proportion- 

ate thrust  increase. 

18.  In  what  way  does  increased  velocity  affect  the  angle  of  incidence? 

19.  What  is  the  purpose  of  the  camber  and  why  should  upper  and  lower 

faces  differ? 

20.  What  is  meant  by  an  airplane's  aspect  ratio? 

) 
/ 


12  Practical    Aviation 


CHAPTER  ANALYSIS 

Elements  of  Airplane  Design 

FACTORS  OF  SUPERIORITY  IN  DESIGN 

(a)  Climbing-  Rate. 

(b)  Greatest  Speed. 

(c)  Horizontal  Equivalent. 

(d)  Design   for   Maximum   Climb. 

(e)  Design   for   Maximum   Velocity. 

ANGLES  OF  INCIDENCE  IN  FLIGHT: 

(a)  Minimum. 

(b)  Optimum. 

(c)  Rest  Climb. 

(d)  Maximum. 


CHAPTER  II 


Elements  of  Airplane  Design 

The  military  aviator  can  insufe  proficiency  only  through  acquisition  of 
a  sound  knowledge  of  the  characteristics  of  design  which  govern  the  con- 
struction of  an  airplane.  Air  tactics  in  warfare,  while  a  subject  for  military 
experts,  are  insolubly  a  part  of  the  mechanics  of  aeronautics.  While  the 
manner  of  conducting  air  battles  is  subject  to  daily  changes,  it  must  be  re- 
membered that  the  effective  observer  or  air  fighter  who  creates  new  evolu- 
tions is  logically  one  whose  knowledge  of  engineering  features  of  design  is 
sound.  Skill  in  manipulation  of  controls  is  essential  of  course,  but  it  can 
readily  be  recognized  that  attempted  creation  of  new  tactics  might  well  be 
fatal  unless  an  aviator  has  an  intelligent  understanding  of  the  limitations  of 
his  machine  and  what  it  can  accomplish  within  the  safety  factor. 

In  this  chapter  some  consideration  will  be  given  to  the  factors  upon 
which  a  military  airplane  must  base  its  superiority. 

In  the  preceding  chapter  fundamental  principles  of  flight  have  been 
given ;  it  now  devolves  upon  the  student  to  recognize  that  in  military  use  of 
flying  machines  two  important  features  are  encountered: 

(a)  Superiority  in  climbing  rate. 

(b)  Greatest  speed. 

It  is  obvious  that  the  machine  which  excels  in  speed  and  ability  for  fast 
climb  will  be  most  effective  against  the  enemy.  An  airplane  which  attains 
speed  at  the  sacrifice  of  climbing  ability  can  be  out-maneuvered  by  fast- 
climbing  enemy  aircraft  in  air  battles,  and  the  same  is  true  of  reverse  quali- 
ties of  climb  versus  speed.  The  combination  of  great  speed  with  maximum 
climb  is  the  ideal  striven  for  in  military  airplane  design. 

As  in  all  mechanical  devices,  however,  the  ideal  must  be  subjected  to 
compromise,  and  it  is  now  purposed  to  apply  the  knowledge  of  fundamentals 
previously  gained  to  consideration  of  the  engineering  factors  which  govern 
the  design  of  machines  for  maximum  climb  and  greatest  velocity. 

Thus  far  the  reader  should  bear  in  mind  that  the  airplane  is  being  studied 
in  two  distinct  divisions;  viz.,  the  lifting  surfaces  and  the  propelling  mech- 
anism, or  (a)  the  airplane  structure,  (b)  engine  and  propeller. 

In  the  preceding  chapter  the  factors  of  lift-drift  ratio  were  outlined  and 
commented  upon.  As  a  thorough  knowledge  of  the  proportion  of  lift  to  drift 
is  essential  to  an  aviator,  further  considerations  of  design  will  be  mentioned. 

13 


14 


Practical    Aviation 


Horizontal    Equivalent 


15 


Figure  10 — Lifting  surfaces  of  same  area  but  different  horizontal  equivalent 


The  efficiency  of  the  airplane  structure  is  determined  by  the  lift-drift 
ratio,  and  an  additional  item  in  relation  to  lifting-  surfaces  which  must  be 
considered  is : 

HORIZONTAL  EQUIVALENT 

This  is  determined  by  the  arrangement  of  lifting  surfaces  and  is  im- 
portant because  lift  (vertical  component  of  the  reaction)  varies  as  the  hori- 
zontal equivalent  of  the  surface,  but  drift  remains  the  same.  That  is,  with 
reduction  in  horizontal  equivalent  (H.  E.)  of  aerofoil  the  ratio  of  lift  to  drift 
is  lessened. 

Figure  10  gives  front  views  of  two  lifting  surfaces. 

Both  have  the  same  surface  area,  but  the  upper,  having  its  full  horizontal 
equivalent,  has  the  best  lift-drift  ratio. 

The  lower  surface,  being  inclined  from  its  center,  has  lessened  H.  E. 
and  in  consequence  less  lift. 

Therefore,  as  the  lower  surface  containing  the  same  area  as  the  upper 
surface,  produces  the  same  amount  of  drift,  but  less  vertical  lift,  its  lift-drift 
ratio  is  less  than  the  upper's. 


Sacrifice  of  efficiency  in  lift-drift  ratio  is  often  made  to  gain  lateral  stability;  such 
employment  of  surfaces  tilted  from  the  center  will  be  considered  later. 


16 


Practical    Aviation 


Large  ong/e  of  fnc/dence 


Figure  11 — Airplane  designed  for  maximum  climb 


Airplane  design  is  restricted  by  opposing  essentials  which  require  the 
aerofoil  (lifting  surface)  characteristics  and  velocity  to  produce  either  Maxi- 
mum Climb  or  Maximum  Velocity.  A  compromise  between  the  two  is  rep- 
resented in  all  airplanes. 

DESIGN  FOR  MAXIMUM  CLIMB 

The  factors  in  an  airplane  designed  for  maximum  climb  are : 

(a)  Large  aerofoil. 

(b)  Low  velocity. 

(c)  Large  angle  of  incidence  to  propeller  thrust. 

(d)  Large  angle  relative  to  direction  of  motion. 

(e)  Large  camber. 

(a)  LARGE  AEROFOIL — A  large  area  of  lifting  surface  is  required  to 
engage  the  mass  of  air  necessary  for  flight  with  a  low  velocity. 

(b)  LOW  VELOCITY— Speed  must  be  sacrificed  to  secure  the  best  lift- 
drift  ratio. 

(c)  LARGE  ANGLE  OF  INCIDENCE  TO  PROPELLER  THRUST- 
The  most  efficient  airplane  is  one  with  inclined  lifting  surfaces  propelled  by  hori- 
zontal thrust,  therefore  a  flying  machine  for  maximum  climb  to  be  driven  along 
an  upward  sloping  path  with  propeller  thrust  horizontal  has  its  aerofoil  at  a  large 
angle  to  the  direction  of  the  thrust. 

See  A — A1  Figure  11. 

In  the  preceding  chapter  it  was  shown  that  the  lift-drift  ratio  falls  with  increased 
velocity  where  the  angle  of  incidence  is  great,  because  with  a  large-angled  aerofoil 
increased  speed  creates  more  eddies  in  the  air  reaction.  These  air  reactions  require 
power  to  produce  them,  yet  they  have  no  lift  value;  they  therefore  represent  drift  and 
lower  the  lift-drift  ratio. 

(d)  LARGE  ANGLE  OF  INCIDENCE  TO  DIRECTION  OF  MOTION 
— With  low  velocity  the  angle's  relation  to  the  direction  of  motion  should  be  large. 

See  A — B,  Figure  11. 

(e)  LARGE  CAMBER — With  low  velocity  and  large  angle  cf  incidence 
the  camber  of  the  aerofoil  should  be  large. 


Design    for    Maximum    Velocity 


17 


S//70//  angte  of  incidence 


Thrust 


Line  of 

,  Horizon  fa/  and 
d/nscf/on  of  motion 


Figure  12 — Airplane  designed  for  maximum  velocity 


The  airplane  designed  mainly  for  speed  has  a  small  margin  of  lift  at 
low  altitudes  when  its  propeller  thrust  is  horizontal.  In  the  rarefied  atmos- 
phere of  higher  altitudes  engine  efficiency  is  lowered  and  the  margin  of 
lift  disappears.  Then  only  horizontal  flight  is  possible.  Flying  thus  with 
its  thrust  horizontal  it  is  at  maximum  efficiency,  if  loss  of  engine  and  pro- 
peller efficiency  is  not  considered. 

DESIGN   FOR  MAXIMUM  VELOCITY 

The  factors  in  an  airplane  designed  for  maximum  speed  with  given 
surface  and  power  are  exactly  opposite  the  requirements  for  maximum 
climb.  Thus : 

(a)  Small  aerofoil. 

(b)  High  velocity. 

(c)  Small  angle  of  incidence  to  propeller  thrust. 

(d)  Small  angle  relative  to  direction  of  motion. 

(e)  Small  camber. 

(a)  SMALL  AEROFOIL — By  its  increased  velocity  the  speedier  propelled 
surface  engages  a  greater  mass  of  air  in  a  given  time  and  the  required  lift  is 
secured  with  smaller  surface. 

(b)  HIGH  VELOCITY— Lessened  aerofoil  angle  produces  less  drift,  and 
velocity  may  be  increased  without  loss  in  lift-drift  ratio. 

(c)  SMALL  ANGLE  OF  INCIDENCE  TO  PROPELLER  THRUST— 
As  both  propeller  thrust  and  direction  of  motion  are  horizontal,  a  small  angle  of 
incidence  is  most  efficient  for  speed. 

(d)  SMALL  ANGLE  OF  INCIDENCE  TO  DIRECTION  OF  MOTION 
— Where  velocity  is  a  consideration  paramount  to  lift,  a  small  angle  of  incidence 
is  most  efficient. 

(e)  SMALL   CAMBER — Lessened  camber  at  high  velocity  produces  the 
best  lift-drift  ratio. 

The  airplane  built  in  accordance  with  the  above  is  intended  to  possess  only  suf- 
ficient lift  to  get  off  the  ground.  The  types  illustrated  on  this  and  the  preceding  page 
are  extremes,  but  the  compromise,  an  airplane  with  climb  and  velocity  made  equal  con- 
siderations, i.e.,  a  practical  all-around  type,  is  designed  by  consideration  of  the  factors 
disclosed  in  these  examples. 


18 


Practical   Aviation 


Figure  13a — Minimum  angle 


Figure  I3b — Optimum  angle 


In  the  illustrations  on  this  page  an  airplane  of  practical  utility  is  shown 
at  varying  angles  of  incidence  while  in  flight. 

At  low  altitudes  the  aircraft  shown  has  slight  margin  of  lift  when  the 
thrust  is  horizontal. 

The  fighting  machine  usually  flies  at  an  altitude  where  maximum  velocity 
is  gained  at  sacrifice  of  maximum  lift.  It  is  obvious  that  with  slight  margin 
of  lift  at  low  altitudes,  the  margin  of  lift  disappears  with  the  rise  of  the 
airplane,  because  of  loss  of  engine  power  in  the  rarefied  air.  But  when  the 
machine  arrives  at  the  altitude  where  horizontal  flight  is  just  possible,  it  is 
given  its  maximum  velocity  because,  even  though  engine  and  propeller 
efficiency  is  lowered,  the  margin  of  lift  has  disappeared  and  the  surfaces  are 
at  their  best  flying  efficiency  for  horizontal  flight. 

ANGLES  OF  INCIDENCE  IN  FLIGHT 

Minimum: — (See  Figure  13a).  The  angle  of  the  aerofoil  is  the  smallest 
at  which,  with  amount  of  power  and  area  of  surface  fixed,  the  machine  can 
maintain  greatest  velocity  in  horizontal  flight  at  low  altitudes. 

An  airplane  having  less  camber  and  smaller  angle  of  incidence,  i.e.,  so  designed 
that  the  margin  of  lift  is  negligible,  or  just  sufficient  to  maintain  horizontal  flight,  would 
attain  greater  velocity  with  the  same  surface  area  and  power. 

Optimum — (See  Figure  13b).  Here  the  axis  of  the  propeller  is  hori- 
zontal and  the  angle  of  incidence  that  which  is  required  for  best  lift-drift 
ratio.  Velocity  is  lessened  at  this  angle,  at  which  slight  climb  is  developed 
at  low  altitudes. 

Best  Climb — (See  Figure  13c).  This  angle  is  about  midway  between 
maximum  and  optimum  angles  of  incidence.  Here  the  increased  angle  has 
added  to  the  drift  and  thereby  decreased  the  velocity. 

With  the  angle  fixed,  a  decrease  in  velocity  lessens  the  drift,  but  where  the  angle 
has  been  increased  the  lift  thereby  gained  in  a  measure  offsets  the  loss  in  lift  through 
lessened  velocity. 

Beginners  should  never  exceed  the  angle  of  best  climb. 

Maximum — (See  Figure  13d).  Horizontal  flight  is  just  possible  at  this 
angle,  because  drift  has  been  greatly  increased  and  velocity  materially  les- 
sened in  consequence. 

//  the  angle  were  further  increased  the  lift-drift  ratio  would  be  so  lowered 
that  the  lift  would  be  less  than  the  weight  and  the  airplane  would  fall.  This 
fall  is  known  as  the  "pancake." 


Figure  13c — Angle  of  best  climb 


Figure  13d — Maximum  angle 


Practical    Aviation  19 


REVIEW    QUIZ 

Elements  of  Airplane   Design 

1.  Why  is  a  knowledge  of  design  valuable  to  the  military  aviator? 

2.  State  the  combination  of  qualities  which  represents  the  ideal  in  mili- 

tary airplanes. 

3.  Define   horizontal   equivalent. 

4.  What    change    is    effected    in   the    lift-drift   ratio    when   horizontal 

equivalent  is  reduced? 

5.  For  what  reason  is  a  sacrifice  of  efficiency  in  lift-drift  ratio  often 

made? 

6.  Name  the  factors  of  design  which  produce  an  airplane  for  maximum 

climb. 

7.  Why  is  a  large  aerofoil  required  with  low  velocity? 

8.  Should  the  aerofoil's  angle  of  incidence  be  great  or  small  for  climb- 

ing? 

9.  What  should  be  its  relation  to  the  direction  of  motion  when  climb- 

ing? 

10.  State  when  an  airplane  designed  mainly  for  speed  is  at  maximum 

efficiency  with  given  motive  power  efficiency. 

11.  Name  the  requirements  of  airplane  design  for  maximum  velocity. 

12.  State  the  reason  why,  with  engine  efficiency  lowered,  certain  air- 

plane surfaces  are  at  their  best  flying  efficiency  at  high  altitudes. 

13.  What  is  meant  by  the  minimum  angle  of  incidence  in  flight? 

14.  What  flight   quality  is   developed   at  low  altitudes  with  optimum 

angle  of  incidence? 

15.  State  the  effect  on  velocity  at  the  angle  of  incidence  for  best  climb. 

What  will  happen  if  the  maximum  angle  is  exceeded? 


20  Practical    Aviation 


CHAPTER  ANALYSIS 

Flight  Stability  and  Control 

AIRPLANE  EQUILIBRIUM: 

(a)  Stability. 

(b)  Longitudinal  Stability. 

(c)  Lateral  Stability. 

(d)  Directional   Stability. 

(e)  Center  of  Gravity. 

LONGITUDINAL  STABILITY: 

(a)  Lifting  Surfaces. 

(b)  Stabilizing  Surfaces. 

(c)  Longitudinal   Dihedral. 

(d)  Canard  Principle. 

(e)  Main  Surface  Dihedral. 

LATERAL  STABILITY: 

(a)  Washout  and  Washin. 

(b)  Ailerons.     . 

(c)  Banking. 

CONTROLS: 

(a)  Wheel  and  Column. 

(b)  Joystick. 


CHAPTER  III 


Flight  Stability  and  Control 


Maintenance  of  airplane  equilibrium  is  secured  by  (a)  features  of  de- 
sign, (b)  controls  operated  by  the  pilot. 

The  following  factors  of  stability  and  control  are  to  be  considered: 

(1)  Stability — The  natural   tendency  of  a  body  disturbed  to  return  to 
normal  position. 

(2)  Longitudinal   Stability — The   tendency   of   an   airplane   to   maintain 
stability  along  the  direction  of  normal  horizontal  flight  and  overcome  pitching 
and  tossing. 

(3)  Lateral  Stability — The  tendency  to  oppose  rolling  sideways. 

(4)  Directional  Stability — The  tendency  to  oppose  swerving  to  the  right 
or  left  of  its  proper  course. 

In  dealing  with  these  factors,  one  must  dispose  of  the  popular  miscon- 
ception that  stability  is  fixed  "steadiness"  in  flight,  attained  through  skillful 
design.  While  not  easily  capsized,  an  inherently  stable  airplane  does  not 
respond  readily  to  its  controls;  it  is  sensitive  to  all  air  disturbances  and  will 
roll  and  sway  in  response  to  air  billows,  whereas  one  of  neutral  stability 
answers  its  mechanical  and  automatic  controls  handily,  and  because  it  has 
no  inherent  tendency  to  hold  a  fixed  position  relative  to  the  air,  adjusts  itself 
easily  so  that  its  position  relative  to  the  ground  is  not  changed  by  air  dis- 
turbances. 

It  is  well  to  remember  that  the  air  is  at  times  treacherous  and  the  air- 
plane should  be  so  designed  that  it  will  sail  through  the  medium  on  an  even 
keel  more  or  less  of  its  own  accord,  yet  not  be  too  sensitive  to  air  disturb- 
ances. Through  actual  participation  in  flight  the  aviator  learns  manipulation 
of  controls  according  to  the  "feel"  of  the  air,  and  this  constitutes  a  large 
part  of  his  training;  it  is  at  once  seen,  however,  that  this  instinctive  handling 
limits  his  usefulness  unless  with  it  goes  an  understanding  of  the  principles 
of  stability  and  control  which  govern  flight. 

21 


22 


Practical    Aviation 


i/ff 


fifcusf 


Figure  14 — Balance  of  forces  for  airplane  equilibrium 


CENTER  OF  GRAVITY 

The  first  consideration  of  airplane  stability  and  general  flying  efficiency 
is  the  center  of  gravity,  for  the  craft  is  suspended  in  the  air  and  rotates  about 
this  point.  The  proper  place  for  its  location  is  where  the  forces  of  thrust, 
resistance,  lift  and  weight  act. 

Ordinarily,  the  airplane  is  so  designed  that  the  thrust  line  passes  nearly 
through  the  center  of  resistance,  and  the  center  of  gravity  is  made  in  line  with 
the  weight  and  lift. 

See  Figure  14. 

The  center  of  thrust  is  often  placed  below  the  center  of  resistance,  for  convenience. 
In  pusher  types  the  thrust  is  sometimes  above  the  line  of  resistance.  The  tendency 
to  .nose  down  thus  produced  is  overcome  by  having  the  center  of  lift  back  of  the  center 
of  gravity.  The  principle  of  coincident  centers  is  the  factor  of  proper  balance,  but 
with  variations  in  the  position  and  strength  of  these  forces  produced  in  flight,  the  bal- 
ance is  restored  by  small  forces,  such  as  the  tail  of  the  airplane. 

If  the  center  of  gravity  is  too  low  it  produces  a  pendulum  effect  and 
causes  a  sideway  roll  of  the  airplane.  When  too  high,  if  disturbed  it  seeks 
a  position  as  far  as  possible  from  the  original,  tending  to  tip  over  the 
airplane. 

METHODS  OF  DETERMINING  THE  C.  G. 

(a)  Point  of  balance  may  be  determined  by  placing  a  roller  under  the  airplane. 

(b)  The  airplane  swung  from   a  point  overhead  and   a  plumb  line  dropped  from 
this  point. 

(c)  With  the  machine  supported  at  front  and  rear,  the  weight  at  each  point   de- 
termined and  the  distance   between   the  two  points  measured.    This  is  known   as   the 
method   of   moments. 


Longitudinal    Stability 


23 


\ 
\ 

D/recf/o/7             ^ 

\^                                      *»% 

\                                                              *N^ 

S^ 

of  •<-—         •••-\ 

\ 

.Center  of  Pressure 

Figure  15  —  Instability  of  cambered  surfaces 

LONGITUDINAL  STABILITY 
LIFTING  SURFACES 

Cambered  wing  surfaces  are  longitudinally  unstable  at  angles  of  inci- 
dence below  12  degrees,  at  which  angles  fair  lift-drift  ratio  is  produced. 

In  Figure  15,  the  centers  of  pressure  of  surfaces  1,  2  and  3  are  indicated. 
The  C.  P.  is  the  point  at  which  all  the  air  forces  about  balance. 

Surface  1  is  cambered  and  in  a  position  approximately  vertical,  moving  in  a  direc- 
tion from  right  to  left.  Its  center  of  pressure  is  along  the  exact  center  of  the  surface. 

With  decrease  in  angle  to  one  of  about  30  degrees,  the  center  of  pressure  moves  for- 
ward to  the  position  shown  in  Surface  2. 

In  Surface  3  the  angle  of  incidence  has  so  decreased  that  there  is  a  downward 
pressure  at  point  A.  Corresponding  depressions  in  such  negative  angles  increase  pro- 
portionately the  pressure  A.  The  center  of  pressure  being  the  resultant  of  all  air  forces, 
it  is  affected  by  the  downward  pressure  at  A  and  moves  backward.  This  pushes  up  the 
rear  of  the  surface  and  increases  the  tendency  to  dive.  But  as  the  surface's  angle  of 
incidence  is  increased  the  pressure  at  point  A  decreases,  whereupon  the  center  of  pres- 
sure moves  forward  and  pushes  up  the  front.  If  the  angle  is  thus  greatly  increased  the 
result  is  a  "tail  slide." 

STABILIZING  SURFACE 

Since  the  cambered  wing  surface  is  inherently  unstable,  a  stabilizing 
surface  at  some  distance  in  the  rear,  or  at  the  tail,  is  added.  This  tail  surface 
has  less  angle  of  incidence. 

Figures  16a,  16b  and  16c  illustrate  the  effect  of  the  tail  surfaces,  the 
upper  portions  of  the  drawing  showing  main  lifting  surfaces  at  varying 
angles,  and  with  tail  attached  in  lower  view. 

In  Figure  16a,  the  lift  force  is  in  rear  of  the  center  of  gravity,  which  tends  to  make 
the  wing  dive;  in  the  lower  view  it  is  shown  how  the  downward  pressure  on  the  tail 
counteracts  this  tendency. 

Figure  16b  shows  a  surface  with  lift  passing  through  the  center  of  gravity.  The 
wing  is  therefore  balanced  and  tail  pressure  is  not  needed  unless  a  sudden  change  in 
angle  is  effected. 

In  Figure  16c  the  line  of  lift  force  is  ahead  of  the  center  of  gravity.  The  tendency 
of  the  wing  to  rear  up  is  offset  by  upward  pressure  on  the  tail;  note  lower  view. 


Center  of 
Grow'ty 


C6.     L 


Center  ofo/vwty 
//// 


Ceaterof 

./Grov/ty 


L  A  ,  C.G. 


Figure   16a 


Figure  166 
Balance  of  lifting  surfaces  by  tail  stabiliser 


Figure  \6c 


24 


Practical    Aviation 


Line  of  wing 
(Qng/e  of  in  defence 


Figure  17 — Dihedral  angle  formed  by  lifting  surfaces  and  stabiliser 

LONGITUDINAL  DIHEDRAL  ANGLE 

The  tail  must  have  an  angle  of  incidence  smaller  than  that  of  the  wings. 
The  angle  of  incidence  of  the  tail  stabilizing  surface  is  ordinarily  about  one- 
third  of  the  aerofoil  angle.  The  neutral  lift  lines  of  each,  when  projected 
to  meet,  make  a  dihedral  angle. 

See  Figure  17. 

Occasionally,  the  tail-plane's  angle  is  the  same  as  that  of  the  main  lifting  surfaces, 
the  lessened  angle  of  incidence  required  of  the  former  being  secured  by  the  downward 
deflection  of  air  from  the  upper  aerofoil. 

To  illustrate  the  effect  of  stability  secured  by  the  longitudinal  dihedral,  we  may 
consider  an  airplane  traveling  a  horizontal  course;  in  this  position  the  thrust  and  direc- 
tion of  motion  are  identical.  The  nose  of  the  machine  then  being  suddenly  deflected 
by  some  air  disturbance,  the  angle  of  incidence  is  changed  with  the  downward  position. 
Assume  that  on  the  horizontal  course  the  aerofoil  angle  was  12  degrees  and  with  the 
deflection  the  thrust  line  is  lowered,  say,  3  degrees.  The  angle  of  incidence  is  not 
changed  in  the  same  proportion,  because  the  momentum  of  the  former  (horizontal) 
course  pulls  it  off  the  direction  of  thrust. 

The  net  change  of  angle  of  incidence  will  be  assumed  to  be  2  degrees.  Both  main 
lifting  surfaces  and  tail  stabilizer  are  affected  by  the  change  because  both  are  fixed 
to  the  airplane  structure.  Both  have  decreased,  proportionately.  The  main  lifting 
surfaces,  with  former  angle  of  incidence  at  12  degrees,  have  decreased  to  10  degrees. 
The  tail  stabilizer,  with  former  angle  0  degrees,  has  now  a  minus  angle  or  negative  of 
2  degrees.  Therefore,  since  the  main  surfaces  have  lost  12  deg. — 2  deg,  or  1/6  of  their 
lift,  and  the  tail  stabilizer  is  now  at  an  entirely  negative  angle,  the  tail  will  fall  faster 
than  the  main  planes.  The  airplane  in  consequence  rights  itself,  or  readjusts  to  the 
former  horizontal. 

The  reverse  happens  when  the  nose  of  the  machine  is  tilted  up  by  a  gust  of  wind. 
While  both  main  lifting  surfaces  and  tail  surface  increase  angles  of  incidence  in  the 
same  amount,  the  angle  (which  determines  the  lift)  increases  in  greater  proportion 
with  the  tail  than  with  the  main  surfaces,  which  lifts  the  tail  faster.  The  airplane  then 
assumes  its  first  position  at  a  slightly  greater  altitude. 

The  variation  of  angle  of  incidence  is  not  as  great  as  the  variation  of  the  airplane's 
angle  to  the  horizontal. 

Stability  produced  by  the  effect  of  the  longitudinal  dihedral  exists  only  when  there 
is  momentum  in  the  original  direction. 

The  stability  adjustments  described  are  taking  place  almost  continuously  in  flight, 
although  not  always  perceptible  to  the  aviator. 


Main    Surface    Dihedral 


25 


/  depression 
or  busf/e  \ 


Figure  18 


Figure   19 — Airplane  of  the  Dunne  type,  with  longitudinal  dihedral 

surfaces 


CANARD   PRINCIPLE 

In  early  types,  such  as  shown  in  the  lower  left  of  the  drawing  on  this 
page,  Figure  18,  it  was  customary  to  place  the  stabilizing  surface  in  front. 
The  tail-first  principle  possessed  obvious  disadvantages,  notably  that  suffi- 
cient longitudinal  stability  could  be  had  only  by  giving  this  a  greater  angle 
of  incidence  than  the  main  lifting  surfaces.  Thus  if  the  wings  had  an  angle 
of  5  degrees,  the  forward  stabilizer  was  set  at  an  angle  of  incidence  of  15 
degrees,  which  gave  poor  lift-drift  ratio  at  high  speeds. 

Low  velocities  were  the  rule  in  the  early  days  and  the  defect  in  design 
was  not  appreciated  until  increased  speeds  were  required.  The  principle  of 
the  forward  stabilizer,  known  as  the  canard,  is  now  obsolete. 

MAIN  SURFACE  DIHEDRAL 

Figure  19  shows  a  view  of  the  Dunne  airplane,  from  the  right  rear.  1'his 
type  has  no  stabilizing  tail  surface,  longitudinal  dihedral  being  given  by  the 
main  surface  having  a  decreasing  angle  of  incidence  toward  the  wing  tips 
and  corresponding  camber.  The  theory  is  that  the  wing  tips  act  as  longi- 
tudinal stabilizers. 

This  design  has  the  following  disadvantages : 

(a)  Departure  from  the  usual  form  of  lifting  surfaces,  in  plan  a  parallelo- 
gram, is  a  mechanical  inferiority,  requiring  additional  strength  of  construc- 
tion.    This  increases  weight. 

(b)  Aspect   ratio   is   lowered  because  the   leading  edge   of  the  aerofoil 
is  not  at  a  right  angle  to  the  direction  of  motion.     Lift  is  lessened  on  account 
of  lowered  aspect. 

(c)  Drift  is  increased  by  the  action  of  the  air  on  the  V-shaped  depression 
in  the  center  of  the  aerofoil.     This  dip  is  pointed  in  the  direction  of  motion 
and  when  the  airplane  is  turned  off  its  course  to  a  direction  which  is  the 
resultant  of  thrust  and  momentum,  or  a  sideways  motion,  the  air  pressure  on 
the  corresponding  side  of  the  V  depression  turns  the  machine  back  on  its 
course.     It  is  obvious  that  the  air  reaction  set  up  by  this  depression  increases 
drift. 

(d)  The  necessity  for  decreasing  the   angle   and  camber  toward   wing 
tips  increases  time^and  cost  of  construction. 

ertical  surfaces  at  the  wing  tips,  as  shown  in  the  drawing,  are  some- 
times added,  set  at  an  angle  producing  the  same  stabilizing  effect.  Drift  is 
increased  by  this  arrangement,  and  efficiency  lowered, 


26 


Practical    Aviation 


Non  sk/d  fins 


Effect  of       f 
excess  pressure  1 


s^ 


Figure  20  Figure  21  Figure  22 

Lateral  stabilising  effect  of  upwardly  inclined  wings 

LATERAL  STABILITY 

Upward  inclination  of  the  lifting  surfaces  gives  a  degree  of  lateral  sta- 
bility, the  wings  forming  a  dihedral  angle.  The  tendency  to  a  sideways  roll 
through  air  disturbance  is  thus  corrected  by  the  lower  wing  gaining  greater 
pressure  or  lift  and  the  consequent  side  slip  restoring  the  machine  to  level 
position. 

In  the  upper  portion  of  Figure  20  is  a  representation  of  a  front  view  of  an  airplane 
in  flight,  lifting  surfaces  having  equal  horizontal  equivalent.  When  the  machine  is  tilted 
sideways,  as  shown  in  the  lower  view,  the  horizontal  equivalent  (H.  E.)  of  the  left 
wing,  now  horizontal,  has  increased ;  a  decrease  is  seen  in  the  right  hand  wing,  the 
lower  wing  in  consequence  rising  through  its  added  lift.  The  airplane  is  thus  restored 
to  its  first,  or  normal,  position. 

The  righting  effect  is  not,  however,  proportional  to  the  horizontal  equivalents  of  both 
wings.  In  the  upper  portion  of  Figure  21  it  is  indicated  that  the  reaction,  when  the  airplane 
is  at  normal  position,  has  a  direction  opposed  to  the  gravity  force,  or  weight,  the  two  forces 
being  evenly  balanced,  or  equilibrium  maintained.  In  the  lower  half  of  Figure  21,  with  the 
airplane  tilted  sideways  the  force  of  reaction  is  at  an  angle  or  not  directly  opposed  to 
gravity  force.  The  direction  of  motion  is  therefore  no  longer  directly  forward,  the  re- 
sultant of  the  thrust  and  momentum  giving  the  added  direction  of  motion  indicated  in 
the  drawing.  The  airplane  is  thus  moving  sideways  while  flying  forward. 

To  be  effective,  the  angle  of  the  lateral  dihedral  must  be  great  enough  to  force  the 
airplane  back  to  equilibrium,  and  overcome  the  tendency  to  turning  caused  by  the  in- 
creased air  pressure  exerted  on  the  keel  surface,  greatest  in  effect  toward  the  tail. 

The  theory  is  advanced,  and  with  some  justification,  that  the  lifting  force  is  derived 
from  the  side-slip  in  the  direction  of  the  lower  wing.  Some  designers  therefore  advo- 
cate for  tractor  biplanes  a  dihedral  angle  for  the  lower  wing  only.  An  increasing 
tendency  toward  this  construction  is  noticeable. 

Figure  22  shows  the  side  slip,  with  non-skid  fins  added  where  excessive 
dihedral  is  needed  to  balance  large  keel  surface. 


Washout    and    Washin 


27 


o//eron 


Sma//ang/e  of  incidence 


Figure  23 — Washout 


Figure  24 — Ailerons  attached  to  lifting  surfaces 


WASHOUT 

An  airplane  tends  to  turn  over  sideways  in  a  direction  opposite  to  that 
in  which  the  propeller  revolves.  The  adverse  effect  of  propeller  torque 
(drift)  is  neutralized  by  giving  the  wing  tip  on  the  £L_!e  not  affected  a  smaller 
angle  of  incidence. 

The  washout  is  shown  in  Figure  23. 

Where  practicable,  the  angle  of  incidence  is  also  increased  on  the  side 
tending  to  fall,  its  lift  thereby  being  increased.  Washin  is  the  term  used 
to  describe  the  increased  angle. 

Washing  out  the  angle  of  incidence  on  both  sides  increases  the  drift,  making  pos- 
sible lessened  angle  for  the  ailerons  (the  lateral  controlling  surfaces  shown  in  Figure 
24)  which  gives  them  better  lift-drift  ratio. 

AILERONS  (WING  FLAPS) 

In  Figure  24,  the  drawing  to  the  extreme  right  shows  the  smaller  angle 
of  incidence  of  the  aerofoil  (lifting  surface)  given  by  washout.  In  compar- 
ing it  with  the  other  aerofoil  (top  center  of  page)  it  is  noted  that  the  ailerons 
attached  to  both  have  the  same  inclination,  although  the  ailerons  of  the  aero- 
foil with  washout  have  considerably  less  angle  of  incidence,  therefore  greater 
efficiency. 

BANKING 

When  an  airplane  is  turned  off  its  course  it  does  not  instantly  proceed 
along  its  new  course.  This  is  due  to  the  momentum  of  the  original  course. 
The  new  direction  is  therefore  the  resultant  of  this  momentum  and  the  thrust, 
and  the  sideways  skid  caused  by  the  centrifugal  force  turns  the  lifting  sur- 
faces away  from  their  proper  horizontal  position,  causing  lessened  lift.  Neu- 
tralization of  this  effect  is  created  by  "banking,"  or  tilting  the  airplane  side- 
ways. 

With  the  angle  of  the  lifting  surface  changed  by  banking,  the  inclination  of  bottom 
of  the  lifting  surface  makes  the  pressure  or  lift  force  a  horizontal  component  of  the 
centrifugal  force.  The  velocity  of  the  skid  is  that  required  to  secure  an  air  pressure 
or  lift  opposite  and  equal  to  the  centrifugal  force  of  the  turn.  The  steepness  of  the 
bank  is  governed  by  the  sharpness  of  the  turn,  increasing  as  the  strength  of  the  centri- 
fugal force. 

It  is  obvious  that  when  banking  the  entire  lift  force  is  no  longer  vertical, 
and  it  is  important  that  it  be  sufficient  to  support  the  weight  of  the  airplane, 
or  it  will  fall.  Speed  is  a  requirement  to  offset  this. 

Pilots  must  not  try  to  climb  while  banking. 

Slight  banking  results  in  skidding,  which  is  easily  corrected. 

Too  steep  banking,  however,  may  result  in  a  side  slip  inward,  which  is  likely 
to  be  followed  by  a  nose  dive. 


28 


Practical    Aviation 


Dep  Control  and  Joy  Stick 


29 


Meet  confrof 
/'for  a/ferons 


foof  far  conf rating 
rudder 


Elevators- 


Figure  25 — Mechanical  means  of  directional  and  lateral  control 


DEP  CONTROL 

The  illustration  above  shows  the  airplane's  mechanical  means  of  directional  and 
lateral  control.  These  comprise  operation  of  the  elevators,  ailerons  (sometimes  called 
"wing  flaps,"  when  attached  to  main  lifting  surfaces  as  shown  in  drawing),  and  the 
rudder. 

All  operate  on  the  principle  of  air  force  derived  from  an  inclined  plane. 

The  elevators  are  controlled,  in  U.  S.  training  machines,  from  the  column  which 
supports  the  wheel,  as  shown. 

The  ailerons,  or  wing  flaps,  for  lateral  control  are  moved  by  the  wheel  in  the 
cockpit. 

The   rudder  is   controlled   by  a  foot  bar. 

The  elevators  are  inclined  up  or  down  to  depress  or  lift  the  tail  of  the  airplane. 

The  ailerons  supply  the  difference  in  angle  to  the  two  tips  of  the  wings,  as 
needed,  causing  one  to  lift  more  than  the  other. 

The  rudder's  action  in  turning  the  machine  is  due  to  the  varying  wind  pressure 
exerted  on  the  sides  when  moved  to  one  side  or  the  other. 

JOY  STICK 

Figure  25b,  at  the  bottom  of  the  page,  shows  the  stick  control  usually  preferred 
for  speed  work,  and  widely  known  to  aviators  as  the  "joy  stick."  Pushing  the  stick 
sideways  toward  a  wing  tip  raises  its  aileron  (wing  flap)  and  deflects  the  aileron  on 
the  opposite  end.  When  the  stick  is  pulled  back  the  elevators  at  the  tail  are  raised, 
and  when  pushed  forward  they  are  dropped. 


Figure  25b — Control  by  joy  stick 


30  Practical    Aviation 


REVIEW   QUIZ 

Flight  Stability  and  Control 

1.  Classify  and  define  stability  as  it  applies  to  airplane  equilibrium 

2.  What  undesirable  qualities  has  an  inherently  stable  airplane? 

3.  State  the  proper  location  for  an  airplane's  center  of  gravity. 

4.  What  is  the  effect  if  the  center  of  gravity  is  too  high?    If  too  low? 

5.  How  is  the  point  of  balance  determined? 

6.  Below  what  angle  are  cambered  surfaces  longitudinally  unstable? 

7.  Why  is  the  tail  stabilizer  necessary? 

8.  Explain  the  action  of  the  tail  surfaces. 

9.  What   is  the   relation  of  the  tail's   angle  of  incidence  to  that  of 

the  wing? 

10.  When  is  the  stability  produced  by  longitudinal  dihedral  effective? 

11.  By  example,  illustrate  the  effect  of  stability  secured  by  the  longi- 

tudinal dihedral. 

12.  Why  was  the  canard,  or  tail-first  construction,  discarded? 

13.  Explain   how  the   Dunne   machine   omitted  the   tail  stabilizer  and 

state  the  disadvantages  of  this  type  of  construction. 

14.  Explain  the  stabilizing  action  of  a  lateral  dihedral. 

15.  Why  is  washout  applied  to  wing  tips? 

16.  Is  the  angle  of  incidence  of  ailerons  affected  by  washout? 

17.  State   the  reason   why   the   airplane   is   "banked"  when   turned  off 

its  course. 

18.  Why  is  steep  banking  dangerous? 

19.  Define  in  detail  the  mechanical  means  for  operating  directional  and 

lateral  control  surfaces  by  foot  bar,  wheel  and  column. 

20.  What  is  the  operation  of  the  "joy  stick"? 


Airplane    Fuselage 


31 


32  Practical    Aviation 


CHAPTER  ANALYSIS 

Materials,  Stresses  and  Strains 

ACTION  ON   MATERIALS: 

(a)  Stress. 

(b)  Strain. 

(c)  Factor  of  Safety. 

STRESS  AND  STRAIN  FORCES: 

(a)  Compression. 

(b)  Tension. 

(c)  Bending. 

(d)  Shearing. 

(e)  Torsion. 

STRENGTH  OF  WOOD  UNDER  STRESS 

(a)  Straightness. 

(b)  Fit. 

(c)  Condition. 

WOOD  FOR  AIRPLANES: 

(a)  Spruce. 

(b)  Ash. 

(c)  Maple. 

(d)  Hard  Pine. 

(e)  Walnut  and  Mahogany. 

(f)  Cedar. 

(g)  Hickory. 

WING  COVERING: 

(a)  Fabric. 

(b)  Dope. 

METAL  FITTINGS  AND  WIRE: 

(a)  Steel. 

(b)  Other  Metals. 

(c)  Wire. 


CHAPTER  IV 


Materials,  Stresses  and  Strains 


The  student  having  now  mastered  the  theory  of  flight  and  the  funda- 
mentals of  design  of  airplane  lifting  surfaces  and  controls,  knowledge  of 
rigging  is  next  in  order. 

As  an  infantryman's  first  care  is  for  his  feet,  and  a  cavalryman  for  his 
mount,  so  must  the  military  aviator  know  his  means  of  locomotion,  his  air- 
plane. The  army  does  not  require  the  dismounted  soldier  to  be  a  chiropodist, 
or  the  cavalryman  a  veterinarian,  no  more  than  the  aviator  is  expected  to 
be  an  expert  mechanic.  But  he  must  know  whether  or  not  his  machine^  is 
in  condition,  and  what  he  may  expect  of  it,  without  recourse  to  another's 
judgment.  With  the  engine  out  of  order  a  safe  landing  can  be  made,  but 
when  something  goes  wrong  with  the  rigging  there  is  trouble  ahead.  Should 
the  rigging  be  wrong,  even  though  nothing  breaks,  speed  is  lessened  and 
stability  and  control  made  less  effective. 

Rigging  an  airplane  properly  presupposes  knowledge  of  the  stresses  it 
is  subjected  to  and  the  strains  which  may  appear.  Airplane  materials  are 
of  the  size  and  weight  which  combine  greatest  strength  and  least  weight.  A 
knowledge  of  them  is  important. 

Stress  is  the  load  which  a  body  bears.  It  is  generally  expressed  thus: 
L  -r-  A  =  S,  where  L  is  the  load,  A  the  square  inches  contained  in  the  cross- 
sectional  area,  and  S  the  resultant  stress.  For  example,  with  an  object  meas- 
uring in  cross-section  3"  X  2"  (an  area  of  6  sq.  in.)  and  required  to  support 
a  total  load  of  12  tons,  the  stress  would  be  12  -f-  6  =  2  tons. 

Strain  is  deformation  produced  by  stress. 

If  a  spar  is  known  to  collapse  under  a  maximum  stress  of  1200  Ibs.,  in  a 
training  machine  it  would  be  subjected  to  no  greater  stress  than  100  Ibs. ;  thus 
where  known  stress  of  an  object  is  1200  Ibs.,  and  the  maximum  stress  it  is 
called  upon  to  endure  is  100  Ibs.,  then  1200  Ibs.  -f-  100  Ibs.  =  12,  representing: 

The  Factor  of  Safety,  which  is  ordinarily  expressed  by  the  resultant  of 
known  collapsing  strength  divided  by  maximum  stress  the  object  is  called 
upon  to  endure. 

33 


34 


Practical    Aviation 


Figure  26 — Compression  and  tension  stresses 
produced  by  wood  bending 


Figure  27 — An  illustration 
of  shearing 


STRESS  AND   STRAIN  FORCES 

Strength  of  materials  must  be  understood  from  the  viewpoint  of  strength 
in  compression,  tension,  bending,  torsion  and  shearing.  For  example,  wire 
is  designed  to  take  tension  but  not  compression,  wood  takes  compression  but 
not  shearing,  bolts  are  liable  to  shearing,  etc. 

Compression — The  stress  of  pressure  produces  a  crushing  strain,  best  exampled 
by  the  stress  on  interplane  struts. 

Tension — The  stress  of  pull,  tending  to  elongation,  exampled  by  all  wires. 

Bending — A  combination  of  tension  and  compression  exampled  by  the  bending  of 
wood,  the  outside  fibres  tending  to  pull  apart,  the  inside  to  go  together. 

Shearing — A  cutting  off  sideways  by  a  pull  such  as  is  exerted  on  an  eyebolt  or  pin. 

Torsion — A  twisting  stress,  a  combination  of  the  forces  of  compression,  tension 
and  shearing,  such  as  is  received  by  the  propeller  shaft. 

Bending — Figure  26  illustrates  how  the  combination  of  compression  and 
tension  stresses  are  produced  by  bending.  The  upper  view  shows  a  straight 
piece  of  wood,  the  top  line  (A),  the  center  line,  or  "neutral  axis"  (C)  and  the 
bottom  line  (B)  being  all  of  equal  length.  In  the  lower  view  the  same  piece 
of  wood  is  bent.  Then  center  line  (C)  is  still  the  same  length,  but  the  top 
line  (A)  is  further  from  the  center  and  therefore  longer.  This  is  due  to  the 
stress  of  tension  producing  the  strain  of  elongation;  the  upper  portion  is 
therefore  in  tension,  which  increases  with  its  distance  from  the  center.  Mean- 
while, the  bottom  line,  under  the  strain  of  crushing  produced  by  the  stress  of 
compression,  has  become  shorter  than  the  center  line.  At  the  center  line, 
therefore,  there  is  neither  tension  nor  compression  and  the  wood  nearest  the 
center  is  under  considerably  less  stress  than  that  near  the  top  and  bottom 
lines.  Thus  the  center  may  be  hollowed  out  without  appreciably  weakening 
the  wood,  which  makes  it  possible  to  save  about  25  per  cent,  of  the  weight 
of  the  wood  used  in  the  construction  of  an  airplane. 

Shearing— In  Figure.  27  a  wire  exerting  pull  on  an  eyebolt  is  shown. 
The  lower  view  illustrates  how  the  stress  may  shear  an  eyebolt. 


Strength    of    Wood 


35 


B 


Figure  28-a  Figure  28-b  Figure  29 

Effect  of  strut  bending  under  stress  Strut  properly  and  improperly  bedded 


STRENGTH  OF  WOOD  UNDER  STRESS 

Upon  the  care  exercised  to  have  struts  kept  perfectly  straight  and  evenly 
bedded  into  sockets  rests  the  strength  of  wood  under  compression.  A  stick 
1  inch  in  diameter  and  36  inches  long,  if  kept  perfectly  straight  can  perhaps 
bear  a  ton  weight  without  breaking,  but  if  it  were  not  straight,  or  had  started 
to  bend,  a  compression  of  50  pounds  would  break  it.  Weight  being  of  the 
greatest  importance  in  airplane  design,  the  wooden  parts  are  kept  as  far  as 
possible  in  direct  compression.  To  save  weight  is  the  aim  of  all  designers 
and  in  consequence  an  airplane's  factor  of  safety  is  ordinarily  low.  The 
required  stresses  for  parts  in  direct  compression  may  be  safely  taken,  how- 
ever, if  they  meet  the  requirements  which  follow: 

Straightness — Spars  and  struts  must  be  perfectly  straight.  Viewed  in  cross-sec- 
tion, these  supporting  members  are  elliptical  in  shape  (stream  lined);  the  center  of 
strength  is  therefore  midway  between  the  points  of  greatest  transverse  width.  If  the 
stress  of  compression  is  not  equally  distributed  about  this  point  the  strut  will  bend, 
because  tension  will  be  created  on  one  side  and  compression  on  the  other.  The  effect 
of  a  strut  bending  is  shown  in  Figures  28-a  and  28-b.  In  the  former  the  wire  stays  are 
taut  and  the  proper  gap  between  wings  maintained.  With  the  strut  bent,  as  in  Figure 
28-b,  the  gap  is  lessened  and  the  wires  have  become  slack,  efficiency  in  flight  being  there- 
by lessened. 

Fit — Struts  and  spars  must  fit  their  sockets  accurately  and  be  bedded  correctly. 
While  snugness  is  essential,  the  wooden  portions  of  the  structure  must  slide  into  their 
sockets  or  fittings  by  pushing;  a  hammer  is  never  required.  The  bottom  should  fit  the 
socket  exactly.  In  Figure  29,  strut  A  is  correctly  bedded;  strut  B  is  not  snug  at  the 
bottom,  in  consequence  of  which  the  compression  stress  is  not  evenly  distributed  about 
the  center  of  strength  and  a  bending  stress  is  produced. 

In  assembly,  the  customary  test  consists  of  painting  the  bottom  of  struts  before  they  are  fitted  to  sockets; 
the  paint  must  be  distributed  over  the  entire  bed  when  strut  is  withdrawn. 

Condition — Struts  and  spars  must  be  undamaged.  If  the  wood  is  scored  or  dented, 
and  the  strut  or  spar  should  be  subjected  to  a  bending  stress,  the  outside  fibres  receive 
the  greatest  strain  (as  explained  on  the  preceding  page)  and  the  collapse  will  come  at 
the  imperfect  point.  Cross  grain,  knots  and  similar  blemishes  are  prohibited  for  the 
same  reason. 

The  wood  must  also  be  well  varnished  to  keep  the  moisture  out.  Variation  in  the 
dampness  of  the  atmosphere  causes  wood  to  expand  and  contract,  the  danger  in  this 
variation  being  that  this  expansion  and  contraction  is  not  evenly  distributed  and  the 
symmetry  of  the  spar  or  strut  is  lost. 


36  Practical    Aviation 


WOOD  FOR  AIRPLANES 

Practically  all  of  the  airplane's  framing  is  constructed  of  wood,  one 
reason  for  this  being  that  flaws  can  easily  be  detected ;  consequently,  wooden 
parts  are  seldom  painted,  preservation  being  secured  by  the  use  of  varnish 
which  brings  out  clearly  any  defects.  Lightness,  strength  and  rigidity  are 
the  prime  requirements  for  flying  machine  construction.  Certain  woods  best 
fulfill  these,  better  in  fact  than  any  metal.  This  may  be  illustrated  by  a  com- 
parison of  spruce  with  aluminum,  lightest  of  the  metals. 

A  cubic  foot   of  spruce  weighs  27  pounds. 

A  cubic  foot  of  aluminum  weighs  162  pounds. 

Tensile  strength  of  spruce  per  square  inch  is  7,900  pounds. 

Tensile  strength  of  aluminum  per  square  inch  is  15,000  pounds. 

Compression  strength  of  spruce  per  square  inch  is  4,300  pounds. 

Compression  strength  of  aluminum  per  square  inch  is  12,000  pounds. 

On  the  cubic  foot  basis,  the  weight  of  spruce  has  a  decided  advantage 
over  metal.  Aluminum's  weight  is  6  times  greater;  brass  about  19  times 
greater;  nickel  and  steel  about  18  times;  copper  about  20  times. 

While  wood  is  not  as  strong  as  steel  of  the  same  size,  the  construction 
of  struts  requires  a  certain  thickness  in  proportion  to  their  unsupported 
length,  so  the  use  of  spruce,  although  it  offers  by  its  size  more  head  resist- 
ance, is  to  be  preferred  because  strength  against  bending  is  secured  with  less 
weight. 

Preferential  woods  for  airplane  work  are  Spruce,  Ash,  Pine,  Maple,  Wal- 
nut, Mahogany,  Cedar  and  Hickory.  The  selection  of  the  right  kind  of 
lumber  is  largely  a  matter  of  experience,  but  the  fundamentals  are  soon  ac- 
quired with  application  to  the  subject. 

Spruce — The  strongest  and  most  generally  satisfactory  material  when  clear  grained, 
straight,  smooth  and  free  of  knot  holes  and  sap  pockets.  Combining  flexibility,  light- 
ness and  strength,  it  is  used  for  struts  and  spars. 

Ash — A  straight-grained  wood,  strong  in  tension,  springy,  but  heavier  than  spruce. 
It  is  used  for  main  spars,  longerons,  engine  supports,  rudder  post,  etc. 

Maple — A  strong  wood  suitable  for  small  parts  such  as  the  blocks  to  connect  rib 
pieces  across  a  spar. 

Hard  Pine — A  tough  and  uniform  wood  adapted  for  the  long  braces  in  the  wings. 

Walnut  and  Mahogany — Uniformity,  hardness  and  finishing  qualities  are  the 
reasons  for  extensive  use  of-  these  woods  for  propellers. 

Cedar — Lightness,  uniformity  and  easy  working  qualities  recommend  this  wood 
for  occasional  use  in  fuselage  covering.  Three-ply  wood,  or  veneers,  are  sometimes  used. 

Hickory — Tough,  hard  and  springy,  this  is  the  favored  material  for  skids  and 
landing  chassis  struts. 

Condensed  Table  of  Weight  and  Strength 
U.  S.  Government  Specifications 


Wood 

Weight  per  cubic 
foot  (15% 
moisture) 

Modulus  of  rupture, 
pounds  per  square 
inch 

Compression 
strength,  pounds 
per  square  inch 

Hickory  

50 

16300 

7300 

Ash  

40 

12700 

6000 

Walnut  

38 

11  900 

6100 

Spruce  

27 

7.900 

4,300 

Linen  and  cord  are  used  for  wrapping  wooden  members  to  increase 
strength  against  splitting;  the  winding  is  made  very  tight  and  treated  with 
"dope"  or  glue  for  waterproofing  and  also  to  increase  the  tightness.  Wooden 
parts  are  ordinarily  ferruled  at  the  ends,  usually  with  copper  or  tin,  to  pre- 
vent the  bolt  pulling  out  with  the  grain,  to  prevent  splitting  and  to  supply 
a  uniform  base, 


Wing    Covering    and    Dope 


37 


Figure  30 — View  of  wing  surface  and  method  of  applying  covering 


WING  COVERING 

Unbleached  Irish  linen,  stretched  rather  loosely  on  the  frame  of  the  wing 
and  then  treated  with  "dope,"  is  the  almost  universal  covering  for  airplane 
lifting  surfaces. 

This  fabric  is  woven  with  the  "warp"  of  the  yarn  lengthwise  and  the 
"weft"  across  the  cloth.  It  tests  to  a  60-pound  tension  on  an  inch-wide  strip, 
and  when  doped  shows  a  strength  of  at  least  70  pounds  per  inch.  It  ordi- 
narily weighs  3^4  to  4^4  ounces  per  square  yard.  Doped  and  finished,  air- 
plane linen  weighs  about  0.10  pound  per  square  foot,  inclusive  of  tape  and 
varnish  for  both  top  and  bottom  faces  of  the  surface. 

Rubberized  fabrics,  formerly  used,  were  discarded  because  of  the  necessity  for 
stretching  them  tightly  by  hand  on  the  frame,  and  because  they  tightened  in  dampness 
and  sagged  in  dry  weather. 

The  strips  of  the  linen  wing  covering  are  sewed  together  by  machine, 
forming  a  bag  which  slips  easily  over  the  framework,  seams  running  diago- 
nally across  the  wing.  Figure  30  illustrates  a  partial  covering  on  the  wing 
framework. 

A  cotton  fabric,  the  new  way  of  spinning  which  is  a  closely  guarded  military  secret, 
has  been  added  to  the  materials  for  wing  covering.  Under  the  most  rigid  tests  it  sur- 
passed in  strength  the  stoutest  linen. 

DOPE 

Dopes  for  coating  linen  wing  coverings  are  of  several  kinds,  but  all  are 
some  compound  of  cellulose  acetate  or  nitrate,  soluble  in  ether  or  in  aceton. 
Through  doping,  the  linen  is  tightened  up  on  the  frame  and  given  a  smooth, 
weather-resisting  finish. 

The  United  States  Army  requires  four  coats  of  nitrate  dope,  this  cover- 
ing being  varnished  with  two  coats  of  spar  varnish  after  the  dope  has  set; 
this  acts  as  waterproofing  and  protects  the  dope  from  peeling.  Doped  fabrics 
are  best  cleaned  by  soap  and  water. 

Trade  names  of  commercial  dopes  include:  Cellon,  Novavia,  Emaillite,  Cavaro  and 
Titanine. 


38  Practical    Aviation 


METAL  FITTINGS  AND  WIRE 
STEEL 

Chrome  nickel  or  vanadium  steel,  specially  heat-treated,  is  often  used  for 
bolts,  turnbuckles  and  pins.  When  parts  are  to  be  bent,  special  care  must  be 
taken  that  the  heating  is  not  done  unequally.  Serious  weakening  may  result- 
Cold  rolled  steel,  used  largely  for  ferrules,  clips  and  fittings  in  airplane 
construction,  is  harder  than  mild  annealed  steel,  works  easily  and  wears  well. 
Its  grain  is  well  marked  and  it  should  be  remembered  that  it  is  weakest 
across  the  grain.  Sharp  bends  should  never  be  made  and,  unless  one  is  fa- 
miliar with  annealing,  any  required  bend  should  be  made  slowly  in  a  vise. 
The  jaws  of  the  vise  should  be  protected  by  thick  copper  pads  to  prevent 
nicking  the  plate. 

OTHER  METALS 

Copper  and  tin  are  used  for  tanks  and  ferrules  of  wire  joints. 

Where    rust    resisting    qualities    are    essential    on    metal    fittings,     "monel"    metal    is 
extensively  used.   It  is  composed  of  60  per  cent  nickel,  35  per  cent  copper  and  5  per  cent  iron. 
Aluminum  is   unreliable  and  is  never  used  in  important  fittings. 


CRYSTALLIZATION    AND    FATIGUE 

Metal  is  subject  to  crystallization  and  fatigue. 

Crystallization — Constant  vibration  and  jarring  which  causes  easy  break- 
age at  a  particular  point. 

Fatigue — Repeated   strains   of   bending   and   twisting   result   in   loss   of 
"springiness"  of  metal,  lessening  its  strength.    This  is  known  as  fatigue. 


WIRE 

Two  types  of  wire   are  used  on  airplanes:   solid-drawn,   for  all  minor 
bracing  purposes;  flexible  cable,  for  control,  flying  and  landing  wires. 

Aviation  wire— This  is  a  single  wire,  piano  grade.  While  it  is  the  strongest  for  its 
weight,  it  forms  kinks  easily  when  coiled  and  may  be  seriously  injured  by  a  blow.  Its 
main  use,  therefore,  is  for  braces  in  the  protected  fuselage  and  wings. 

Aviator  strand — This  is  7  or  19  wires  stranded  together  and  used  for  tension  wires 
because  of  its  elasticity,  permitting  it  to  be  bent  around  parts  of  small  diameter. 

Tinned  aviator  cord — This  is  a  cord  or  rope  stay,  composed  of  seven  strands  of  7 
or  19  wires  twisted  into  a  rope.  The  wires  are  galvanized  as  a  protection  against  rust, 
but  where  the  heat  required  for  galvanizing  will  injure  hard  or  small  wires,  they  are 
tinned.  It  is  in  general  use  for  controls,  and  although  less  strong  as  the  same  size 
in  single  wire,  has  the  advantage  of  not  being  seriously  injured  by  a  single  weak  spot. 


Practical    Aviation  39 


REiVIEW  QUIZ 

Materials,  Stresses  and  Strains 


1.  Why    is    a    knowledge    of    strength    of    materials    valuable    to    the 

aviator? 

2.  Define  stress  and  give  an  example  with  an  object  of  definite  area 

supporting  a  given  weight. 

3.  What  is  strain? 

4.  By  an  example,  explain  the  factor  of  safety. 

5.  Briefly  state  the  difference  between  the  forces  of  compression,  ten- 

sion, bending,  shearing  and  torsion. 

6.  How  is  it  possible  to  hollow  out  wooden  parts  without  appreciable 

weakening? 

7.  State  the  value  of  direct  compression  upon  struts. 

8.  Give  the  reason  for  the  care  exercised  in  keeping  struts  straight. 

9.  How  should  a  strut  be  bedded? 

10.  Why  is  it  important  that  struts  or  spars  should  not  be  scored  or 

dented? 

11.  Of  what  value  is  varnish? 

12.  In    what    respects    is    spruce    superior    to    aluminum    for  airplane 

framing  ? 

13.  Explain  how  wooden  members  are  given  increased  strength  against 

splitting. 

14.  What  material  is  generally  used  for  wing  covering? 

15.  How  is  the  covering  made  and  placed  on  the  framework? 

16.  What  is  the  purpose  of  dope  and  what  is  its  composition? 

17.  Give  some  commercial  names  of  dope. 

18.  In  bending  chrome  nickel  or  vanadium  steel  what  caution  should 

be  exercised?   Cold  rolled  steel? 

19.  Define  crystallization  and  fatigue. 

20.  State  the   composition  and   uses   of  aviation  wire,   aviator  strand, 

tinned  aviator  cord. 


40  Practical    Aviation 


CHAPTER   ANALYSIS 

Rigging  the  Airplane 

ERECTION  AND  ASSEMBLY: 

(a)  Landing  Gear. 

(b)  Horizontal  Stabilizer, 

(c)  Vertical  Stabilizer. 

(d)  Rudder. 

(e)  Elevators. 

ASSEMBLY  OF  LIFTING  SURFACES 

(a)  Center  Section. 

(b)  Main  Wing  Section. 

(c)  Assembly. 

ALIGNMENT: 

(a)  Landing  Gear. 

(b)  Wings  Without  Stagger. 

(c)  Staggered  Wings. 

(d)  Main  Wing  Sections. 

(e)  Dihedral  Angle. 

(f)  Angle  of  Incidence. 

(g)  Droop. 

(h)    Controlling  Surfaces. 
(i)     Over-All  Adjustments. 

CONTROL  CABLES  AND  WIRES: 

(a)  Adjustment  of  Controls. 

(b)  Turnbuckles. 

(c)  Cables. 

(d)  Wire  Loops. 

(e)  Tightening  Wires. 

EFFECT  OF  ALIGNMENT  ERRORS: 

(a)  Directional  Stability. 

(b)  Lateral  Instability. 

(c)  Longitudinal   Instability. 

FLIGHT  DEFECTS: 

(a)  Poor  Climb. 

(b)  Lessened  Speed. 

(c)  Poor  Control. 

(d)  Uncontrollable  on  Ground. 


\      CHAPTER   V 

Rigging  the  Airplane 

With  a  thorough  understanding  of  the  fundamental  factors  that  make 
for  flight  efficiency,  practical  rigging  of  the  machine  may  be  turned  to  in  full 
confidence  of  doing  a  good  job.  Reasonable  familiarity  with  the  use  of  simple 
tools  remains  to  be  acquired ;  but  this  is  a  short  process  of  practice  in  their 
handling,  the  keystone  of  success  being  the  exercise  of  care.  If  the  prelimi- 
nary study  has  been  conscientious  up  to  this  point,  the  reason  for  each  step 
in  assembly  will  be  clear  without  explanation  and  the  requisite  exactness 
will  follow  as  a  matter  of  course. 

Golden  Rules  of  Rigging 

Don't  hurry.      If  the  job  is  a  rush  one,  make  haste  slowly. 
Never  lay  tools  on  the  planes. 

Pliers  or  wrenches  are  not  for  use  on  airplane  bolts ;  a  burred  thread, 
or  one  damaged  in  any  way,  should  be  discarded. 

Turnbuckles  are  to  be  started  from  both  ends. 

There  should  be  a  cotter  pin  for  every  nut  and  safety  wires  should  lock 
all  pins  and  turnbuckles. 

Wire  with  a  kink  in  it  should  be  brought  to  the  attention  of  some  one 
in  authority. 

Don't  hammer  or  pound  bolts  and  pins  into  position;  they  must  go  into 
place  by  pushing  or  gentle  tapping. 


(c)   Committee  on  Public  Information 

Figure  31— Assembling  and  rigging  U.  S,  Army  airplanes  at  a  flying  Held 

41 


42  Practical    Aviation 


Figure  32a — Method  of  attaching  land-  Figure  32b — Method  of  attaching  horizon- 

ing  gear  tal  stabilizer 

ERECTION  AND  ASSEMBLY 

An  assembled  airplane  is  a  trim  and  fairly  hardy  machine,  but  before 
assembly  the  parts  are  fragile.  When  received,  the  greatest  care  should  be 
exercised  in  unpacking  boxes  and  crates. 

The  order  of  assembly  and  directions  follow : 

Landing  Gear — Mount  the  wheels  on  the  axle  and  bolt  them  into  place. 
Connect  up  the  tail  skid  by  pinning  the  front  end  to  the  spring  fitting  and 
the  other  end  to  the  socket  of  the  tail  post.  Now  raise  the  fuselage  to  receive 
the  landing  gear.  This  may  be  accomplished  by  blocking,  or  by  tackle  as 
shown  in  Figure  32a,  where  a  line  is  passed  under  the  sills  of  the  engine  bed 
— nowhere  else — and  caught  by  the  hook  of  the  hoisting  block.  Raise  the 
front  end  of  the  fuselage  until  the  lower  clips  of  the  longeron  line  up  with 
the  clips  on  the  ends  of  the  landing  gear  struts.  The  bolts  are  then  passed 
through  the  aligned  holes  and  the  nuts  drawn  up  tight.  Cotter-pins  are  in- 
serted in  the  holes  drilled  through  the  bolt,  which  then  appear  just  beyond 
the  castle  of  the  nut.  The  leaves  of  the  cotter-pins  are  turned  backward, 
locking  the  nuts  in  place.  The  gear  should  then  be  aligned  in  accordance  with 
instructions  on  page  44. 

Horizontal  Stabilizer — With  the  landing  gear  attached  to  the  fuselage, 
elevate  the  tail  of  the  machine,  supporting  it  on  a  horse  of  proper  height,  or 
block  until  the  upper  longeron  is  level,  verifying  the  arrangement  by  use  of 
a  spirit  level  placed  on  the  upper  longeron  at  the  tail.  See  Figure  32b.  Bolt 
the  horizontal  stabilizer  to  the  top  longeron  and  tail  post  and  draw  all  nuts 
tight  and  secure  them  with  cotter-pins. 

Vertical  Stabilizer — Fasten  the  vertical  stabilizer  by  bolting  it  through 
the  forward  part  of  the  horizontal  stabilizer  and  the  clip  at  the  front  of  the 
vertical  stabilizer;  tighten  nuts  and  lock  with  cotter-pins.  A  double  clip  in 
the  rear  passes  over  the  two  bolts  which  fasten  the  horizontal  stabilizer  to 
the  tail  post.  Attach  the  flexible  wire  cables  and  tighten  by  the  turnbuckles. 

Rudder — Attach  the  control  braces  so  that  the  upper  tips  point  toward 
the  line  of  the  hinge.  Mount  the  rudder  on  the  tail  post  and  vertical  stabil- 
izer and  insert  the  pins  in  the  hinges,  securing  them  with  cotter-pins. 

Elevators — Attach  the  control  braces  in  the  same  manner  as  with  the 
rudder  and  mount  the  elevators  on  the  horizontal  stabilizer  by  means  of  the 
hinges  and  pins,  the  latter  being  secured  by  insertion  of  cotter-pins  in  the 
holes  drilled  for  that  purpose. 


Assembly  of  Lifting  Surfaces 


43 


(c)    Committee   on   Public  Information 


Figure  34 — Curtiss  strut  numbering 


brac/ng  wires 
f-  f tying  wires 
L  '  landing  w'res 


Figure  33 — Assembly  of  center  section 


Figure  35 — Method  of  wiring 


ASSEMBLY  OF  LIFTING  SURFACES 

Center  Section — The  section  of  wing  surface  first  attached  is  that  which 
is  directly  over  the  fuselage  and  known  as  the  engine  section  panel.  With 
the  struts  fitted  into  the  proper  sockets  of  the  wing  surface,  the  entire  section 
with  bracing  wires  attached,  is  lifted  and  set  into  the  sockets  on  the  upper 
longeron.  Bracing  wires  are  then  attached  and  the  section  aligned. 

The  method  is  clearly  shown  in  the  photograph,  Figure  33. 

Main  Wing  Sections — While  the  upper  lifting  surfaces  may  be  first  as- 
sembled to  the  engine  section  and  the  lower  wing  then  attached,  it  is  prefer- 
able to  complete  assembly  of  the  sections,  or  panels,  before  attaching  them 
to  the  fuselage.  The  advantage  of  the  latter  method  is  that  less  adjustment 
is  required  and  the  correct  stagger  and  dihedral  is  secured. 

Figure  34  shows  the  numbering  of  struts  on  the  Curtiss  JN-4.  These 
may  be  quickly  committed  to  memory  by  noting  that  the  four  struts  of  the 
center,  or  engine  section  panel,  are  not  designated,  and  that  beginning  at  the 
left  from  the  pilot's  seat,  the  eight  remaining  struts  are  numbered  from  1  to  8. 
The  main  struts  bear  a  number  and  can  easily  be  read  from  the  pilot's  seat;  it  is 
therefore  at  once  evident  ifs  through  error,  a  strut  is  inverted. 

Assembly — The  upper  wing  of  the  left  lifting  surface  receives  struts  Nos. 
1  and  2  in  the  proper  sockets.  The  wires  are  then  connected  to  right  and  left 
by  clips  and  adjusted  by  turnbuckle  until  the  spars  are  straight.  The  wing  is 
then  set  on  a  cushioned  block,  leading  edge  down.  See  Figure  31. 

The  lower  left  wing  is  then  brought,  leading  edge  resting  on  cushioned 
block,  to  a  space  equal  to  the  length  of  the  struts.  Diagonal  wires  are  loosely 
connected  and  spars  inserted  in  sockets,  5  and  6,  and  bolted  into  place. 

The  "landing,"  or  single,  wires  and  the  "flying,"  or  double,  wires  of  struts 
1  and  5  are  then  connected  closely,  so  the  wings  may  be  held  together  while 
being  attached  to  the  fuselage. 

Figure  35  clearly  indicates  the  wiring  of  the  assembled  airplane  wings. 

The  erection  of  the  wing  must  be  done  with  special  care.  Lifting  by  the 
struts  or  edges  of  the  wings  may  result  in  a  serious  strain.  Boards  placed 
under  the  beams  of  the  wing  framework  should  be  used  for  carrying. 


44 


Practical    Aviation 


Figure  37a 


Figure  37b — Stagger  alignment 


ALIGNING  THE  AIRPLANE 


Correct  alignment  oi  an  airplane  is  of  tremendous  importance.  Its  flying 
efficiency  depends  largely  upon  exactness  in  truing  up  all  controls  and  wires 
and  securing  proper  angle  of  incidence  and  dihedral.  The  parts  should  be 
aligned  in  regular  order  as  follows: 

Landing  Gear — To  be  aligned  before  wings  are  attached  to  fuselage.  The  axle  should  be  parallel 
with  the  lateral  axis  of  the  fuselage.  Ascertain  the  exact  center  of  the  fuselage  and  the  axle;  with  spirit 
level  align  the  cross  width  of  the  fuselage.  Drop  a  plumb  line  from  the  center  of  the  fuselage  and  adjust 
the  cross  wires  until  it  is  in  the  exact  center  of  the  axle. 

Or,  if  plumb  bob  and  litre  are  not  available,  adjust  the  cross  wires  so  that  the  measurement  A-B  is 
exactly  equal  to  the  measurement  C-D  in  Figure  36.  The  adjustment  is  made  on  both  front  and  rear  sup- 
ports of  the  under  carriage. 

The  landing  gear  and  fuselage  are  aligned  in  the  factory,  but  their  correctness  should  be  determined 
by  the  method  just  given.  Before  aligning,  it  is  well  to  verify  that  the  tail  support  still  holds  the  fuselage 
horizontal. 

Center  Section — The  bracing  wires  (A-B,  C-D,  Figure  37a)  are  left  sufficiently  tightened  to  keep  the 
struts  straight,  while  the  wings  are  being  aligned. 

Without  Stagger — The  upper  longerons  of  the  fuselage  being  horizontal,  the  struts  are  properly 
placed  when  they  form  a  right  angle.  Adjust  the  sides  first  and  then  the  front.  Check  the  perpendicular 
alignment  by  measuring  off  an  equal  distance  on  the  upper  longeron  back  and  forward  of  some  point  on 
the  bottom  of  the  strut;  the  strut  will  be  exactly  perpendicular  when  the  distance  from  these  two  points  to 
the  top  of  the  strut  measures  exactly  the  same.  Tighten  bracing  wires  evenly  until  sides  and  front  are  cor- 
rectly aligned;  i.  e.,  until  the  measurement  of  corresponding  points  on  cross  wires  are  identical. 

Staggered — The  angle  of  strut  fittings  and  sockets  serves  as  a  guide  to  the  degree  of  stagger.  The 
airplanes  specifications  state  the  stagger;  for  example  in  the  Curtiss  JN-4  it  is  105^j  inches.  This  is 
checked  by  a  plumb  line  suspended  from  the  leading  edge  of  the  top  surface,  as  in  Figure  37b,  and  the 
measurement  is  taken  between  points  A-B ;  that  is,  the  plumb  line  should  be  10-Kj  inches  in  advance  of  the 
leading  edge  of  the  lower  wing. 

In  all  types  of  airplanes  the  specifications  state  how  the  measurements  should  be  taken  (a)  along  the 
line  of  the  chord,  or  (b)  horizontally. 

When  the  stagger  is  verified,  the  wires  should  be  tightened  and  the  cross  distances  measured  until  one 
side  corresponds  exactly  with  the  other.  Side  wires  should  be  adjusted  first,  and  then  the  front,  and  cross 
distances  measured  until  they  correspond  exactly. 

Main  Wing  Sections — The  first  point  to  determine  is  whether  leading  edges  of  the  upper  and  lower 
wing  surfaces  are  exactly  in  line  with  the  center  section.  Standing  on  a  step  ladder,  15  feet  to  one  side, 
a  sight  by  eye  is  taken  along  the  leading  edge  of  the  upper  plane.  If  not  straight,  the  adjustment  for  warp 
or  bow  is  made  by  tightening  or  loosening  the  front  landing  wires.  The  same  should  then  be  done  for  the 
lower  plane  and  the  opposite  wing  aligned  in  the  same  manner.  When  the  cross  wire  adjustments  have 
been  completed,  a  sight  taken  from  both  ends  of  the  wings  should  show  all  struts  in  line  and  parallel  with 
the  center  section  struts. 


Aligning    the    Airplane  45 


76  {'String 


•f  V 

:i   / 


Sptrit  level\        ;A 

Straight^    j1^ 

edge 


Figure  38 — Dihedral  angle  measurements  Figure  39 — Angle  of  incidence 

DIHEDRAL  ANGLE 

One  method  of  securing  the  dihedral  angle  is  shown  in  Figure  38,  where  Ta  is  a  tack 
placed  in  the  exact  center  of  the  center  section,  on  the  leading  edge  of  the  upper  wing.  The 
exact  distance  is  measured  off  then  on  each  side  and  tacks,  Tb,  Tc,  placed  in  the  leading  edge 
of  both  upper  wings,  at  a  point  near  their  tips.  A  string  is  stretched  tightly  between  Tb  and 
Tc.  The  specifications  are  then  referred  to  and  the  dihedral  angle  checked.  Assuming  the 
dihedral  angle  to  be  176  degrees,  then  each  wing  has  been  raised  2  degrees.  The  natural 
sine  of  2°  being  0.0349,  this,  multiplied  by  the  distance  between  Tb  and  Ta  (or  Ta  and  Tc} 
gives  the  proper  distance  between  Ta  and  the  string  directly  above  it. 

Example : 

The  distance  Tb-Ta  (or  Ta-Tc)  is  16  feet=192  inches. 

192  in.X0.0349=r6.7  in.,  or  the  proper  distance  between  Ta  and  the  string  above,  if 

wings  are  set  at  the  proper  dihedral. 

In  making  the  alignment,  wings  should  be  raised  equally  until  the  correct  measurement 
over  the  center  section  is  secured,  with  leading  edges  kept  straight. 

All  adjustments  should  be  made  by  altering  the  wires  from  the  inside  bays;  when 
diagonal  wires  are  to  be  tightened  make  sure  that  the  opposite  wires  in  the  same  bay 
are  slackened  off. 

Check  up  the  alignment  by  measuring  (Figure  38)  from  Ta  successively  to  points  D,  B, 
C,  E,  making  certain  that  the  distance  Ta-B  corresponds  with  Ta-C,  and  Ta-D  is  the  same 
as  Ta-E.  This  will  show  that  both  wings  are  the  same  height. 

ANGLE  OF  INCIDENCE 

The  specifications  give  a  set  measurement  for  the  angle  of  incidence.  Verify  the 
horizontal  position  of  the  top  longeron  of  the  fuselage,  i.  e.,  make  certain  that  the  air- 
plane is  in  flying  position.  Then  place  the  straight-edge  underneath  the  center  of  a 
rear  strut  as  shown  in  Figure  39.  With  a  spirit-level,  adjust  the  straight-edge  to  hori- 
zontal position.  Refer  to  the  specifications  and  note  the  set  measurement  given;  this 
will  require  measurement  from 

(a)— the  lowest  part  of  the  leading  edge  to  top  of  the  straight-edge,  or 

(b) — the  center  of  the  front  strut  to  the  top  of  the  straight-edge. 

This  measurement  must  be  repeated  under  every  strut,  or  the  lower  surface  where 
struts  occur. 

The  measurement  should  not  be  made  between  struts,  because  the  wings  may  be 
slightly  warped. 

If  the  angle  is  too  great: 

Slacken  all  the  wires  attached  to  the  top  of  the  rear  strut  and  tighten  all  the 

wires   attached   to   the   bottom. 

If  the  angle  is  too  small: 

Slacken   all   wires' attached  to   the  bottom   of  the   strut  and  tighten  all  wires 

attached  to  the  top. 

The  correct  adjustment,  laid  down  in  the  specifications,  should  be  made  with  no 
greater  variation  than  1-16  inch.  The  measurements  at  all  struts  must  agree,  i.  e.,  the 
angle  of  incidence  all  along  the  wing  must  be  the  same,  unless  the  wings  have  a  wash- 
out or  washin. 

Check  up  the  stagger  with  a/  plumb  line  to  see  that  it  has  not  been  disturbed  while 
securing  the  dihedral.,  -» 


46 


Practical    Aviation 


Figure  40 — Aileron  rigging 


Figure  41 — Over-all  check 


been  adjusted,  one 
the  propeller,  where 


DROOP 

When  the  angle  of  incidence  and  the  stagger  have 
wing  must  be  slightly  drooped  to  correct  for  the  torque  of 
a  single  propeller  is  used  in  tractor  airplanes. 

With  a  propeller  that  turns  to  the  right  (clockwise)  the  left  wing  is  drooped.    If  it 
turns  to  the  left  the  right  wing  is  drooped. 

For  machines  up  to  100  horsepower,  the  outer  rear 
wing  which  is  to  be  drooped  is  slackened  until  the  trailing 
and  intermediate  struts  is  about  1  inch  lower  than  the  rest 


landing  wire  of  the 
edge  between  outer 
of  the  trailing  edge. 


CONTROLLING  SURFACES 

Since  the  pilot  depends  upon  the  manipulation  of  controlling  surfaces  to 
manage  his  airplane,  exceptional  care  should  be  taken  that  ailerons,  eleva- 
tor and  rudder  are  properly  rigged. 

Ailerons,  Trailing  Edge  (wing  flaps) — With  the  control  levers  rigidly  blocked  into 
neutral  position,  the  aileron  should  be  rigged  so  its  trailing  edge  is  about  Y\  inch  below 
the  trailing  edge  of  the  surface  to  which  it  is  attached.  In  flight  the  angle  of  incidence 
of  the  surface  will  cause  it  to  lift  a  little  above  the  position,  or  to  the  true  line.  This 
is  illustrated  in  Figure  40  where  the  dotted  outline  shows  the  position  during  flight. 

A  basis  of  measurement  commonly  used  is  ^2  inch  depression  for  every  18  inches  of 
chord  of  the  controlling  surface. 

Tail  Stabilizer — With  the  weight  of  the  tail  supported  by  the  tail  skid,  align  the 
rear  edge  of  the  stabilizer  so  it  is  straight  and  parallel  with  the  lateral  axis  of  the  air- 
plane. Take  a  sight  from  the  rear  to  the  leading  edge  of  the  upper  plane,  which 
should  be  in  alignment  with  the  trailing  edge  of  the  stabilizer.  Tighten  the  wires  by 
turnbuckles. 

Elevator  Flaps — With  the  controls  in  neutral  position  adjust  the  control  wires  by 
turnbuckles  until  the  elevator  flaps  are  in  the  same  plane,  and  sufficiently  tight  to 
eliminate  lost  motion. 

Rudder — Adjust  the  control  wires  by  turnbuckle  until  both  foot  bar  and  rudder  in 
neutral  position  show  no  lost  motion  in  control. 

Over-All  Adjustments — Figure  41  illustrates  the  measurements  which  are  taken 
as  a  final  check.  The  measurement  A-B  must  equal  A-C  within  l/g  inch.  Point  A 
is  the  center  of  the  propeller  (in  pusher  types,  the  center  of  the  nacelle)  and  B  and  C 
are  points  marked  on  the  outer  spars  equally  distant  from  the  butts  of  the  spars. 
The  measurement  should  be  taken  from  both  top  and  bottom  on  each  side. 

D-F  should  equal  E-F  within  ^  inch.  The  rudder  post  is  point  F,  and  D  and  E 
are  points  on  the  rear  struts  marked  as  in  the  case  of  B  and  C.  Two  measurements, 
top  and  bottom,  are  also  taken  here. 


Adjustment  of  Control  Cables  and  Wires 


47 


® 


-,.  Not  less  than  4  turns 
'"nor  more  than  5  turns 


Figure  42  —  Turnbuckles,  cables  and  wire  loops 


CONTROL  CABLES  AND  WIRES 

Adjustment  of  Controls  —  From  the  pilot's  seat  move  the  control  levers 
and  note  if  a  quick  movement  shows  lag  or  snatch  in  the  movement  of  the 
control  surfaces.  Movement  of  y%  inch  to  either  side  should  produce  corre- 
sponding motion  of  the  controlling  surfaces. 

Turnbuckles—  The  turnbuckle,  which  is  shown  in  Figure  42a,  is  a  barrel 
with  an  eye-bolt  screwed  into  each  end  ;  it  is  therefore  hollow  and  should  not 
be  turned  with  pliers.  It  is  best  adjusted  by  passing  a  piece  of  wire  through 
the  hole  in  the  center  and  using  it  as  a  lever.  The  illustration  shows  the 
proper  method  of  using  the  locking  wire,  so  the  barrel  may  not  turn  and 
thereby  throw  the  airplane  wires  out  of  the  fine  adjustments  required. 

Cables  —  Windings  must  be  even  with  a  stream-lined  effect  at  the  end 
of  the  winding  as  shown  in  Figure  42b.  The  dimensions  of  the  winding 
before  it  tapers  off  (see  A,  in  the  illustration)  must  be  at  least  15  times  as 
great  as  D,  the  diameter  of  the  cable.  Only  non-acid  flux  should  be  used  in 
soldering. 

Correct  Winding  for   C  ables 
Breaking 


Size  of  Cable 
Inches 
1-32 
1-16 
3-32 
7-64 


Length  of 

Winding 

Inches 


13/4 

2 


Strength 

Pounds 

185 

500 

1,100 

1,600 

2,100 


Size  of  Cable 

Inches 

5-32 

3-16 

7-32 


YA 

5-16 


Length  of 
Winding 
Inches 


43,4 


Breaking 

Strength 

Pounds 

3,200 

5,500* 

6,100 

8,000 

12,500 


*For  cable;  loop  strength  is  5,100  pounds. 

Control  cables  wear  and  fray  out  by  friction  with  pulleys;  careful  exam- 
ination should  be  made  after  each  flight,  and  if  a  single  strand  is  broken 
the  cable  should  be  replaced. 

WIRE  LOOPS 

Wherever  a  loop  is  made  with  wire  to  connect  with  a  fitting  or  turn-buckle  it 
should  be  symmetrical  in  shape  and  reasonably  small,  with  well  defined  shoulders.  A 
loop  properly  made  is  shown  at  the  left  of  Figure  42c,  and  one  improperly  made  at 
the  right.  Where  the  shoulder  is  not  properly  made  and  the  loop  elongated  the 
ferrule  is  likely  to  slip  up  and  throw  the  wire  out  of  adjustment. 

When  the  loop  is  finished  the  wire  should  be  undamaged.     Wire  bent  to  the  degree 
shown   at  -the  lower  end  of  Figure  42c   should  be   discarded. 
TIGHTENING   WIRES 

Care  must  be  exercised  that  wires  are  not  too  tight  or  extra  loads  will  be  placed 
on  spars  and  struts.  Wires  should  never  be  at  a  tension  so  they  "sing." 


48  Practical    Aviation 


THE  EFFECT  IN  FLIGHT  OF  ALIGNMENT  ERRORS 
DIRECTIONAL  STABILITY 

Wrong  Angle  of  Incidence — The  airplane  will  turn  toward  one  side  if 
the  angle  of  incidence  of  one  side  of  the  wing  surface  or  tail  surface  is  wrong; 
for  drift  increases  with  greater  angle  and  decreases  with  lessened  angle. 

Fuselage,  Rudder-fin  or  Struts  Off  Line  of  Direction  of  Flight— The  air- 
plane will  turn  off  its  course,  for  unless  these  are  aligned  they  will  act  as  a 
rudder. 

Distorted  Surfaces — The  airplane  will  turn  off  its  course  if  there  is  an 
improper  bend  in  leading  or  trailing  edge  or  spars,  for  the  amount  of  drift 
will  be  changed  on  one  side  by  increased  resistance, 

LATERAL  INSTABILITY 

Wrong  Angle  of  Incidence — If  the  angle  of  one  wing  is  greater,  more 
lift  will  be  produced  on  that  side,  with  corresponding  decrease  on  the  other 
wing.  The  airplane's  tendency  will  then  be  to  fly  one  wing  down. 

Distorted  Surfaces — The  same  tendency  to  fly  one  wing  down  will  be 
observed  when  the  camber  of  the  wing  surfaces  is  spoiled  by  some  distor- 
tion, through  which  the  lift  is  made  unequal. 

LONGITUDINAL  INSTABILITY 

Wrong  Angle  of  Incidence — If  the  lifting  surface  angle  is  too  great  the 
nose  will  rise  through  excess  of  lift  and  a  tendency  to  fly  tail  down  will  re- 
sult. Too  small  an  angle  may  cause  the  airplane  to  fly  nose  down. 

Occasionally,  the  tail  plane's  angle  of  incidence  is  found  to  be  wrong;  the  angle 
should  be  lessened  if  the  airplane  is  nosing  down,  and  increased  if  tail-heavy.  Adjust- 
ments of  this  kind  must  be  made  with  care,  because  longitudinal  stability  depends  en- 
tirely on  the  tail-plane  having  less  angle  than  the  main  lifting  surfaces. 

Fuselage  Warped — For  the  reason  given  above,  a  fuselage  warped  up  or 
down,  thereby  giving  an  incorrect  angle  of  incidence  to  the  tail  plane,  may 
result  in  the  airplane  nosing  down  or  being  tail  heavy. 

Wrong  Stagger. — A  nose-heavy  airplane  will  result  if  the  top  wing  is 
not  staggered  forward  to  the  correct  degree,  because  the  lift  will  then  be  too 
far  back.  An  error  of  y^  inch  will  make  a  material  difference  in  longitudinal 
stability.  The  cause  of  such  error  is  generally  due  to  the  elongation  of  wire 
loops  or  if  wires  have  pulled  the  fittings  into  the  wood, 

FLIGHT  DEFECTS 
POOR  CLIMB 

Excepting  engine  and  propeller  trouble,  the  reason  for  an  airplane 
climbing  badly  is  generally  due  to  (1)  too  small  angle  of  incidence;  (2) 
distorted  surfaces. 

LESSENED  SPEED 

Excepting  engine  and  propeller  trouble,  poor  flight  speed  is  generally 
due  to  (1)  too  great  angle  of  incidence;  (2)  distorted  surfaces;  (3)  skin- 
friction,  from  dirt  or  mud  on  surfaces. 

POOR  CONTROL 

The  main  causes  are  (1)  incorrect  setting  of  control  surfaces;  (2)  dis- 
tortion of  control  surfaces ;  (3)  control  cables  badly  tensioned. 

UNCONTROLLABLE  ON  GROUND 

When  an  airplane  will  not  "taxi"  straight  the  fault  is  generally  due  to 
(1)  improper  alignment  of  landing  gear,  wobbly  wheels,  or  (2)  unequal  ten- 
sion of  shock  absorbers. 


Practical    Aviation  49 


REVIEW  QUIZ 

Rigging  the  Airplane 

1.  Give  six  important  cautions  about  handling  tools. 

2.  Explain  the  process  of  assembling  the  landing  gear. 

3.  What  control  is  first  attached  to  the  fuselage,  and  how? 

4.  How  is  the  vertical  stabilizer  fastened? 

5.  Explain  the  assembly  of  rudder  and  elevators. 

6.  What  section  of  the  wing  surface  is  first  attached  to  the  fuselage? 

7.  Should  main  wing  sections  be  assembled  complete  before  attaching? 

8.  State  how   struts   are   numbered   and   a  reason  why  numbering  is 

essential. 

9.  Give  in  detail  the  process  of  wing  assembly  with  particular  refer- 

ence to  the  initial  adjustment  of  wires. 

10.  Why  is  careful  alignment  of  an  airplane  important? 

11.  What  are  the  two  methods  of  aligning  the  landing  gear? 

12.  Describe  wing  alignment  without  stagger. 

13.  What  is  the  check  for  staggered  wings? 

14.  State  how  the  alignment  of  main  wing  sections  is  verified. 

15.  Explain  the  method  which  insures  correct  dihedral  angle. 

16.  Where  and  with  what  aids  should  the  measurement  be  taken  for  the 

angle  of  incidence? 

17.  What  adjustment  is  made  to  correct  for  torque  of  the  propeller? 

18.  Give  a  rule  for  rigging  the  trailing  edge  ailerons. 

19.  From  what  points  are  final  check  measurements  taken? 

20.  State  seven  general  rules  which  govern  adjustment  of  cables,  wire 

loops  and  turnbuckles. 


50  Practical    Aviation 


CHAPTER    ANALYSIS 

Fundamentals  of  Motive  Power 

THE  PROPELLER: 

(a)  Balance. 

(b)  Surface  Area. 

(c)  Length. 

(d)  Straightness. 

(e)  Care. 

THE  GASOLINE  ENGINE  CYLINDER: 

(a)  Combustion  Chamber. 

(b)  Piston. 

(c)  Connecting  Rod. 

(d)  Crank  Shaft. 

(e)  Revolution. 

THE  FOUR-CYCLE  PRINCIPLE: 

(a)  Intake  Stroke. 

(b)  Compression  Stroke. 

(c)  Power  Stroke. 

(d)  Exhaust  Stroke. 

MULTIPLE  CYLINDER  ENGINES: 

(a)  4-cylinder  Operation. 

(b)  6-cylinder  Operation. 


CHAPTER  VI 


Fundamentals  of  Motive  Power 


Earlier  chapters  have  dealt  entirely  with  the  theory  of  flight  and  the 
function  and  construction  of  the  airplane  as  a  flight  medium.  The  student 
is  now  ready  to  consider  the  propulsion  of  the  machine,  upon  which  all  theory 
of  flight  obtains. 

Flight  is  made  possible,  as  has  already  been  explained,  by  the  action  of 
the  air  on  inclined  surfaces  driven  through  the  air  at  high  velocity.  The 
reader  is  aware  that  the  driving  force  is  a  propeller  actuated  by  a  gasoline 
engine.  Consideration  of  the  propeller  will  be  brief,  as  the  military  aviator 
is  not  concerned  with  the  details  of  engineering  mathematics  upon  which  pro- 
peller efficiency  is  based.  Some  knowledge  of  the  method  of  checking  up  the 
balance  of  the  air  screw  is  all  that  is  required  of  the  pilot,  and  this  is  given 
on  the  page  following. 

The  study  of  engines  must  necessarily  be  of  a  general  character,  as  the 
varying  types  of  design  in  iniernal  combustion  engines  make  a  full  considera- 
tion of  the  refinements  of  operation-  a  subject  of  voluminous  proportions.  The 
four  chapters  devoted  to  airplane  motors  give  all  the  important  points  of 
information  in  a  brief  survey  of  the  general  construction  and  operation  prin- 
ciples which  apply  to  the  most  familiar  types  of  aviation  engines. 

The  aviation  engine  must  have  small  weight  per  horse  power,  minimum 
head  resistance  and  reliability  of  operation;  for  these  reasons  some  minor 
changes  in  design  from  familiar  automobile  types  will  be  noticed.  The  first 
consideration  is  the  stationary  water-cooled  motor;  later,  the  rotary  air- 
cooled  types  will  be  described. 

The  student  aviator  is  specially  cautioned  to  apply  himself  to  mastery 
of  this  chapter  on  engine  theory.  A  thorough  working  knowledge  of  motors 
is  required  of  military  airmen  before  flight  instruction  is  begun.  A  pilot  who 
does  not  understand  the  principles  of  his  motor's  operation  can  never  expect 
to  secure  the  best  efficiency  from  his  engine,  and  the  ability  to  secure  an 
extra  ounce  of  motive  power  or  speed  is  often  the  means  of  gaining  a  victory 
over  an  enemy  airplane.  Special  emphasis  is  laid  on  the  explanation  of  the 
four-cycle  principle  in  this  chapter ;  without  a  full  understanding  of  these 
phases  of  operation  the  study  cannot  be  continued  intelligently. 

51 


52 


Practical   Aviation 


(c)    Committee  on  Public  Information 

Block  test  of  an  airplane  engine  with  propeller  attached,  showing  the  screen  protection  given 

to  the  mechanician.    The  necessity  for  this  precaution  Is  at  once  obvious  when 

It  Is  known  that  the  propeller  revolves  at  a  speed  of  1,400  revolutions 

per  minute 


The    Propeller 


53 


Pitch 


Pitch 


(Roller 
/     f  Level 


£  Blade  _.  4  B/ade 

figure  43 


f/gure  44 


Figure  44  b 


Figure  43 — Action  of  propeller  revolutions 
Figures  44,  44b — Method  of  propeller  test  for  balance  and  area 

THE  PROPELLER  OR  "AIR  SCREW 

The  propeller's  revolutions  represent  thrust,  its  action  in  screwing 
through  the  air  (see  Figure  43)  translating  the  power  of  the  engine  into  for- 
ward motion.  The  drift  of  the  airplane,  due  to  its  resistance,  is  overcome  by 
opposition  of  the  thrust ;  it  follows,  therefore,  that  the  power  of  the  propeller 
thrust  must  be  greater  than  the  airplane's  drift,  or  the  velocity  will  decrease. 

BALANCE 

The  propeller  is  mounted  after  the  airplane  is  assembled.  It  should  first 
be  tested  for  balance,  for  if  one  blade  is  heavier  than  the  other  it  will  vibrate 
when  run  on  the  engine.  The  usual  test  is  shown  in  Figure  44.  A  stand  is 
leveled  up ;  a  roller  is  then  inserted  in  the  hub  of  the  propeller,  which  turns 
freely  on  the  roller ;  this  roller  is  then  allowed  to  roll  freely  on  the  level.  Any 
lack  of  balance  is  thus  easily  detected. 

Another  method  is  indicated  in  Figure  44b.  The  propeller  is  placed  in  horizontal 
position  and  three  points  on  the  blades  measured  off  equally  distant  from  the  center. 
By  means  of  a  spring  balance  weighing  scale,  the  weights  are  taken  at  these  points, 
and  must  correspond  for  each  side. 

Application  of  more  varnish  on  the  lighter  side  is  usually  sufficient  to  equalize  a  pro- 
peller out  of  balance. 

SURFACE  AREA 

Measurement  of  three  equi-distant  points  by  callipers  should  show  cor- 
responding measurements  to  exactness  of  less  than  %  inch.  Figure  44b  illus- 
trates this  measurement,  A  being  equal  to  A',  B  to  B'  and  C  to  (7. 

LENGTH 

Blades  should  be  of  equal  length  to  1-16  inch. 

STRAIGHTNESS 

With  the  propeller  mounted  on  a  shaft  an  object  should  be  fixed  in  a 
position  where  the  tip  of  one  blade  grazes  it.  With  the  point  marked,  the 
other  blade  is  brought  around  and  should  come  within  ^  inch  or  graze  it. 

CARE  OF  PROPELLERS 

They  should  never  be  leaned  against  a  wall  or  allowed  to  remain  long  in  horizontal 
position. 

They  should  not  be   stored  either  in  very  damp,  or  very  dry,  places. 

They  should  not  be  stored  where  the  sun  will  shine  on  them. 

The  proper  method  of  storage  is  hanging  in  vertical  position  on  horizontal  pegs. 


54 


Practical    Aviation 


(c)    Committee  on  Public  Information 

This  picture,  take-   at  one  of  the  "Ground  Schools"  of  the  Army  Signal  Corps,  well  illustrates 
the  earnestness  and  concentration  of  the  men.    The  instructor  is  obviously  having  no  dif- 
ficulty in  keeping  his  men  at  work,  for  these  future  American  airmen  know  just  as  well 
as  he  how  vital  it  is  that  they  should  understand  every  impulse  of  the  engine  which 
will  soon  mean  so  much  to  them  in  midair.   A  most  thorough  and  fundamental 
course  of  training  in  engines  is  necessary  for  the  men  who  carry  the  respon- 
sibility for  America's  warfare  in  the  skies 


The    Gasoline    Engine    Cylinder 


55 


Water  outlet 


Rocher  arm 


Valve  spring 

haust  yalvs 
^-Combust ton  chamber 


Connecting  rod 


Crank  shaft 


Crank  case 


Connecting  rod  be0nng 


Figure  45 — Single  cylinder  of  a  gasoline  engine 

THE  GASOLINE  ENGINE  CYLINDER 

Vaporized  gasoline  mixed  with  air  and  set  afire  by  an  electric  spark  re- 
sults in  combustion  (explosion),  the  intense  heat  from  which  develops  the 
pressure  which  operates  the  engine. 

Figure  45    shows   a   single   cylinder   of  a  gasoline   engine   in   sectional   view.     The 
names  of  the  parts  should   be   studied. 
COMBUSTION    CHAMBER 

The  closed  end  of  the  cylinder,  in  which  the  combustion  takes  place,  is  known  as  the 
cylinder  head,  the  space  between  it  and  the  piston  being  the  combustion  chamber. 
PISTON 

This  is  a  cylindrical-shaped  body  which  slides  back  and  forth  in  the  cylinder,  the 
combustion  (explosion)  driving  it  downward. 
CONNECTING  ROD 

Suspended  from  the  piston  is  a  connecting  rod  which  acquires  a  reciprocating  motion 
as  the  piston  moves  up  and  down. 
CRANK  SHAFT 

The  connecting  rod  is  attached  to  the  crank  shaft,  by  means  of  which  the  reciproca- 
ting motion  is  changed  to  a  rotary  motion  (as  a  wheel  revolving  on  its  axis)   which  turns 
the  propeller. 
REVOLUTION 

A  complete  turn  of  the  crank  shaft,  moving  the  piston  down  and  back,  is  called  a 
revolution. 


56  Practical    Aviation 


THE  FOUR-CYCLE  PRINCIPLE 

There  are  two  types  of  internal  combustion  engines  using  gasoline  for 
motive  power;  viz.:  the  two-cycle  and  the  four-cycle.  These  may  be  distin- 
guished by  considering  them  as  two-stroke  and  four-stroke  engines.  The  two- 
cycle  engine  has  no  valves,  the  gas  entering  and  exhausting  through  ports 
in  the  cylinder  walls,  covered  and  uncovered  at  proper  intervals  by  the  travel 
of  the  piston  up  and  down.  The  four-cycle  engine,  which  will  be  considered 
exclusively  in  the  text  following,  as  its  use  is  almost  universal  in  aviation,  has 
intake  and  exhaust  valves  operated  by  mechanical  means. 

Figures  46,  47,  48  and  49  show  the  action  of  the  four-cycle  engine,  clearly 
indicating  the  operations  during  the  four  strokes. 


INTAKE  STROKE 

Suction  caused  by  the  piston  starting  downward,  as  the  engine  is  "cranked,"  draws 
the  explosive  gasoline  vapor  into  the  combustion  chamber  of  the  cylinder.  It  enters 
through  the  intake  valve,  which  is  the  only  opening.  The  exhaust  valve  is  closed,  the 
intake  valve  being  so  adjusted  that  the  cam  opens  it  mechanically  as  the  suction  action 
of  the  piston  commences. 


COMPRESSION  STROKE 

Both  valves  are  closed  as  the  piston  starts  on  its  up-stroke  and  the  explosive  mixture 
in  the  cylinder  is  compressed  into  the  small  space  of  the  combustion  chamber  as  it 
reaches  the  top  of  the  stroke. 

The  explosive  value  of  compression  may  be  illustrated  by  considering  the  action 
of  gunpowder,  which,  ignited  in  the  open  air  burns  slowly  but  is  instantly  exploded  if 
confined  to  a  small  chamber. 

POWER  STROKE 

As  the  piston  reaches  the  top  the  spark  is  timed  to  jump  the  spark  gap  points  and 
ignite  the  explosive  vapor.  The  piston  is  driven  down  by  the  expansion  of  the  gas, 
making  the  power  stroke. 

EXHAUST  STROKE 

As  the  piston  returns  from  the  power  stroke  the  exhaust  valve  is  opened,  the  pres- 
sure from  the  explosion  forcing  out  the  burned  gas.  The  upward  move  of  the  piston 
pushes  out  all  of  the  burned  gas  that  does  not  escape  by  its  own  pressure. 

The  exhaust  valve  closes  as  the  piston  reaches  the  top,  and  the  inlet  valve  opens  to 
admit  a  fresh  charge  of  gas  into  the  cylinder.  The  operation  is  then  repeated  as  long  as 
the  engine  runs. 


The    Four-Cycle    Principle 


57 


Figure  46 


Figure  47 


figure  46 


Figure  46 — Intake  stroke 


Figure  47 — Compression  stroke 
Figure  49 — Exhaust  stroke 


figure  49 


Figure  48— Power  stroke 


THE  FOUR-CYCLE  PRINCIPLE 


FIGURE  46 

This  is  the  intake  stroke.    The  inlet  valve  is  open  and  the  gas  is  entering  the  cylin- 
der, drawn  by  the  suction  of  the  piston. 
FIGURE  47 

This  is  the  compression  stroke.    Both  valves  are  closed  and  the  piston  is  returning, 
the  upward  stroke  compressing  the  gas. 
FIGURE  48 

This  is  the  power  stroke.    The  electrical  spark  from  the  spark  plug  ignites  the  gas. 
Both  valves  are  closed  as  the  combustion  drives  the  cylinder  downward. 
FIGURE  49 

This  is  the  exhaust  stroke.     Only  the  exhaust  valve  is  open,  the  upward  movement 
of  the  piston  forcing  the  burned  gases  out  of  the  cylinder. 


58 


Practical    Aviation 


Figure  50 — Cross  section  of  a  4-cy Under  engine 


MULTIPLE  CYLINDER  ENGINES 

A  cycle  operation  requires  four  strokes  to  two  revolutions.  Only  one  of  the  four 
strokes  is  a  power  stroke ;  therefore,  in  a  single  cylinder  engine  the  piston  must  be  car- 
ried through  three  dead  strokes.  This  ordinarily  requires  a  heavy  fly  wheel,  which  when 
started  will  continue  to  revolve.  It  is  obvious  that  the  more  cylinders  an  engine  has  the 
steadier  will  be  the  power  impulses,  since  the  successive  explosions  may  be  timed  to 
follow  so  closely  that  one  of  the  pistons  will  always  be  on  a  power  stroke.  Thus  in  avia- 
tion engines  where  weight  is  a  material  factor,  the  heavy  fly-wheel  is  dispensed  with  by 
use  of  multiple  cylinder  engines. 

4-CYLINDER  OPERATION 

Four-cylinder  engines  deliver  a  power  impulse  every  stroke,  or  two  power  impulses 
to  every  revolution. 

Figure  50  ihr-vs  a  4-cyKnder  engine  in  cross  section. 

It  will  be  n  ed  that  the  crank  shaft  which  delivers  motion  to  the  propeller  is  set 
at  180  degrees,  the  end  pair  being  a  half-revolution  from  the  inside  pair. 

As  piston  No.  1  descends  on  the  power  stroke,  No.  2  is  coming  up  on  exhaust;  No. 
3  is  ascending  on  compression  and  will  be  fired  next;  No.  4  is  taking  in  gas. 

FIRING  ORDER 

The  rotation  in  which  the  explosions  take  place  in  the  cylinders  is  therefore  1,  3,  4,  2. 

This  engine  could  as  well  fire  1.  2,  4,  3,  but  it  will  be  obvious  that  explosions  in  the 
order  1,  2,  3,  4  would  require  a  crank  shaft  alternately  projecting  to  each  side,  1  and  3 
being  up  when  2  and  4  are  down.  This  construction  has  the  following  disadvantages: 

(a)  A  crank  shaft  weaker  and  more  difficult  to  make. 

(b)  A  rocking  motion,  or  vibration,  from  side  to  side. 

The  alternate  distribution  of  power  impulses,  when  cylinders  are  fired  in  the  order 
shown  in  the  illustration,  makes  for  smooth  running. 


Multiple    Cylinder    Engines 


59 


Figure  51 — Cross  section  of  a  6-cy Under  engine 


6  Cylinder  Motor 

Figure  52 — Graphic  illustration  of  cylinder 
operation  in  4-  and  6-cyIindcr 


6-CYLINDER  OPERATION 

The  6-cylinder  engine  is  four-cycle,  the  same  as  the  4-cylinder  engine.  The  principal 
differences  in  construction  are  in  the  addition  of  more  cylinders  and  consequent  change 
in  crank  shaft. 

Figure  51  shows  a  cross  section  of  the  6-cylinder  engine. 

It  will  be  noted  that  the  crank  shaft  is  arranged  to  turn  two  revolutions  during  four 
strokes,  as  in  the  case  of  the  4-cylinder  engine.  The  crank  shaft  is  therefore  divided 
into  three  pairs  of  throws,  i.e.,  each  pair  is  placed  at  120  degrees,  or  1-3  of  a  circle 
apart.  The  pairs  are:  1  and  6,  2  and  5,  4  and  3. 

FIRING  ORDER 

In  Figure  51,  cylinder  No.  5  has  just  fired,  No.  3  will  fire  next,  after  which  the 
order  will  be  6,  2,  4,  1. 

With  4-cylinder  engines  an  explosion  takes  place  each  half-revolution;  the  6-cylin- 
der engine  in  the  same  half-revolution  has  l1/^  explosions.  That  is,  power  impulses  are 
continuous  in  6-cylinder  engines,  in  fact  they  overlap;  this  results  in  smooth  running. 

Figure  52  is  a  graphic  representation  of  the  sequence  of  cylinder  operation  in 
4-cylinder  and  6-cylinder  types  of  engines,  showing  how  power  impulses  overlap  in  the 
latter. 


60 


Practical   Aviation 


(c)   Committee  on  Public  Information 

The  construction  of  the  lower  half  of  the  crank  case  and  the  method  of  supporting  the 
crank  shaft  are  clearly  shown  in  this  photograph.  An  interesting  feature  of  the  illustration 
is  the  cradle  in  which  the  crank  case  rests;  it  is  so  constructed  that  the  successive  assembly 
of  engine  parts  may  be  made  and  the  engine  turned  around  so  as  to  be  at  any  angle  with 
the  floor.  Since  the  introduction  of  this  cradle  the  mechanician  is  no  longer  required  to 
lie  on  his  back  and  work  upwards 


Practical    Aviation  61 


REVIEW  QUIZ 

Fundamentals  of  Motive  Power 

1.  What  is  the  aerodynamic  force  which  the  power  of  the  propeller 

thrust  must  overcome? 

2.  How  is  a  propeller  tested  for  balance?    Give  two  methods. 

3.  When  a  propeller  is  out  of  balance  how  is  the  lighter  side  usually 

equalized? 

4.  State  how  surface  area  measurement  of  the  propeller  is  taken. 

5.  What  is  the  test  for  straightness? 

6.  Give  four  rules  for  care  of  propellers. 

7.  Explain  how  the  motive  force   is  produced  in  the  cylinder   of  an 

engine. 

8.  Name  and  define  three  moving  parts  which  transmit  the  motion. 

9.  State  the  difference  between  a  two-cycle  engine  and  a  four-cycle 

engine. 

10.  Describe  in  detail  the  four  phases  or  operations  of  the  four-cycle 

engine. 

11.  What  operating  advantage  is  gained  by  increasing  the  number  of 

cylinders? 

12.  How  many   power  impulses  per  revolution  are  delivered  by  a  4- 

cylinder  engine? 

13.  In  a  4-cylinder  engine,  at  what  degree  angle  are  crank  throws  set? 

14.  Explain  why  the  four  cylinders  are  not  fired  in  successive  order. 

15.  In  what  important  particular  does  the  6-cylinder  engine  differ  from 

the  4-cylinder? 

16.  How  are  the  throws  of  the  crank  shaft  arranged  for  six  cylinders? 

17.  Give  a  proper  firing  order  for  a  6-cylinder  engine. 

18.  In  a  half -revolution,   how  many   explosions  take  place  in  the  six 

cylinders? 

19.  State  an  advantage  gained  when  power  impulses  overlap. 

20.  Compare   the   sequence   of   operation   in   4-cylinder   and   6-cylinder 

engines. 


62  Practical    Aviation 


CHAPTER  ANALYSIS 

Pistons,  Valves  and  Carburetors 

THE  PISTON: 

(a)  Construction. 

(b)  Piston  Rings. 

(c)  Connecting  Rod. 

(d)  Wrist  Pin. 

CRANK  SHAFT: 

(a)  Construction. 

(b)  Attachments. 

CRANK  CASE: 

(a)  Construction. 

(b)  Mountings. 

VALVES  AND  VALVE  MECHANISM 

(a)  Camshaft. 

(b)  Cams. 

(c)  Exhaust  Valve. 

(d)  Inlet  Valve. 

(e)  Valve  Operating  Mechanism. 

(f)  Valve  Clearance. 

CARBURETION: 

(a)  Principle  of  the  Carburetor. 

(b)  Construction. 

(c)  Duplex. 

(d)  Manifolds. 


CHAPTER  VII 


Pistons,  Valves  and  Carburetors 


Continuing  the  subject  of  aviation  engines,  a  few  considerations  may  be 
noted,  preliminary  to  the  study  of  pistons,  valves  and  carburetors. 

Fir?/-  is  the  refinement  of  design  necessary  for  aeronautical  work.  The 
aviation  engine,  unlike  those  of  motor  cars,  ordinarily  uses  75  per  cent,  of 
its  horsepower,  as  against  one-quarter  usage  in  motor  cars. 

A  second  consideration  of  design  is  the  necessity  for  building  an  aviation 
engine  as  light  as  possible,  yet  the  punishment  of  material  within  the  engine 
structure  is  about  fourteen  times  as  severe  as  in  the  motor  car.  The  effect 
is  demonstrated  in  the  respective  lives  of  both  types.  A  motor  car  engine 
generally  runs  up  to  a  mileage  of  25,000,  at  a  maximum  average  speed  of  25 
miles  per  hour,  or  completes  1,000  hours  operation  before  overhauling  is 
necessary.  The  aviation  engine,  with  a  speed  of  100  miles  an  hour,  requires 
a  complete  overhaul  in  about  50  flying  hours,  a  total  of  5,000  miles,  or  one- 
fifth  of  the  motor  car's  mileage. 

These  comparisons  broadly  illustrate  the  relative  severity  of  the  two 
types  of  engine  service.  But  although  it  is  required  that  the  aviation  engine 
be  of  light  construction,  strength  must  not  be  sacrificed  in  vital  parts.  While 
light  weight  is  the  aim  in  designing  the  crank  shaft  and  crank  case,  main 
bearings,  crank  and  piston  bearings,  strength  is  maintained  by  very  careful 
selection  of  materials. 

An  airplane  required  to  make  climbs  of  20,000  feet  must  necessarily  have 
perfect  reliability  of  operation.  The  structure  of  the  aircraft  is  obviously  sen- 
sitive to  vibration  and  an  engine  which  does  not  function  smoothly  materi- 
ally impairs  flight  efficiency.  Irregular  impulses  of  the  engine  also  affect  its 
light  structure  and  uniform  explosions  are  a  requisite.  This  uniformity  is 
gained  only  through  perfect  distribution  of  gas  to  the  cylinders. 

The  student  should  keep  these  conditions  in  mincl  as  the  study  of  vital 
parts  of  the  engine  is  continued. 

63 


64 


Practical   Aviation 


A- Piston  with 
connect  ing  rod 


C*  con  centric 
piston  ring 


D-  eccentric 
piston  r/ng 


Figure  53 — Details  of  the  piston  and  connecting  rod 
PISTON 

Although  one  of  the  simplest  parts  of  the  airplane  motor,  the  piston  is 
one  of  the  most  important,  as  it  receives  the  full  force  of  the  explosion  and 
transmits  the  gas  combustion  into  power. 

In  construction,  it  shows  only  slight  variations  in  the  numerous  types  of  engines;  the 
most  common  form  of  construction  is  shown  at  A  and  B  in  Figure  53.  The  piston  is  made 
usually  of  cast  iron,  steel  or  aluminum,  machined  to  fit  the  cylinder  diameter  with  a  clearance 
of  .005  to  .010  of  an  inch  to  compensate  for  the  expansion  of  heat  and  permit  lubrication 
between  it  and  the  cylinder  walls.  The  clearance  varies  with  the  designed  speed  of  the  motor, 
increasing  for  the  higher  speed  motors  in  which  greater  friction  is  created.  Channels  are 
cut  in  the  outer  face  of  the  piston  wall,  near  the  top ;  in  these  the  piston  rings  are  placed. 

PISTON  RINGS 

These  are  split  rings  of  cast  iron,  sprung  so  as  to  bear  tightly  against  the 
wall  of  the  cylinder  to  prevent  leakage  of  gas  from  the  combustion  chamber 
and  the  passage  of  lubricating  oil  into  the  explosion  area.  Two  types  are 
shown  at  C  and  D  in  Figure  53,  and  the  common  forms  of  expansion  joints 
at  E  and  F. 

CONNECTING  ROD 

The  connecting  rod  joins  the  piston  to  the  crank  shaft  and  transmits  the 
motion  to  the  latter  as  the  piston  travels  up  and  down.  It  is  usually  made 
of  drop  forged  steel,  I-beam  construction. 

A  typical  connecting  rod  is  shown  at  H  in  Figure  53,  which  indicates  the  two  bearings, 
the  upper,  of  bronze,  connected  to  the  wrist  pin,  and  the  lower  bearing,  through  which  the 
crank  shaft  passes,  usually  split  and  made  of  a  bronze  base  with  babbitt  metal  carefully 
scraped  to  exact  clearance. 

WRIST  PIN 

This  fitting,  also  known  as  the  gudgeon  or  piston  pin,  joins  the  piston  to 
the  connecting  rod.  As  shown  at  G  in  Figure  53,  it  is  a  simple  cylindrical 
element,  usually  made  of  steel  and  fitting  the  bosses  closely. 


Crank   Shaft  and   Crank  Case 


65 


Gears  drwng. 
oil  pump 


Baffle  plate 


0/1  pump  ' 


Figure  54  (upper) — Crank  shaft  of  6-cy Under  engine 
Figure  55  (lower) — Lower  section  of  crank  case  with  shaft  in  position 


CRANK  SHAFT 

As  the  main  drive  shaft  of  the  motor,  the  crank  shaft  is  subjected  to 
greatest  strain;  it  is  therefore  ordinarily  made  of  high  tensile  steel,  drop  or 
machine  forging.  It  is  constructed  as  a  bar  having  U-shaped  offset  arms,  or 
crank-throws,  one  for  each  cylinder,  for  attachment  to  the  connecting  rods. 
It  is  usually  drilled  for  oil  ducts  and  hollowed  to  reduce  weight,  yet  is  of 
requisite  strength  to  withstand  the  continuous  shocks  it  sustains. 

A  crank  shaft  for  a  6-cylinder  engine  is  shown  in  Figure  54,  with  four  of  the  con- 
necting rods  attached  and  the  propeller  hub  and  flange  shown  at  the  right  end.  The 
opposite  end  carries  a  gear  which  meshes  with  a  system  of  gears  to  transmit  motion  to 
the  camshaft,  magneto,  oil  pump  and  other  auxiliary  parts. 

In  the  illustration  provision  is  made  for  mounting  the  propeller  on  the  crank  shaft 
for  direct  drive,  in  which  case  a  flywheel  would  not  ordinarily  be  used.  Because  the 
speed  of  the  motor  is  generally  considerably  higher  than  the  most  efficient  number  of 
revolutions  per  minute  of  the  propeller,  reduction  gears  are  commonly  introduced  at  the 
propeller  end  of  the  crank  shaft  where  the  motor  speed  exceeds  1,400  revolutions  per 
minute. 

CRANK  CASE 

The  crank  case  is  usually  made  of  aluminum  alloy,  in  two  parts,  the 
upper,  to  which  the  cylinders  are  bolted,  and  the  lower  containing  the  crank- 
shaft and  lubricating  oil.  It  contains  the  crank  shaft  bearings,  or  seats,  in 
which  the  center  line  of  the  crank  shaft  is  supported.  These  mountings  are 
usually  made  of  babbitt  or  other  high  anti-friction  metal. 


Figure  55  shows  the  lower  half  of  a  typical  crank  case  for  a  6-cylinder  engine,  the 
shape  of  the  case  conforming  to  the  type  of  the  motor  in  each  instance. 


66 


Practical    Aviation 


Driving  gear     Corns        Reorteanng 


Valve 
/spring 


Cam  shaft 
-'.....-Cam 


Figure  56  (upper  left) — Camshaft,  showing  the  driving  gear  and  cams 

Figure  57a   (lower  left) — Valve  operating  mechanism  for  overhead  valves 

Figure  57b  (right) — Valve  operating  mechanism  where  camshaft  is  at  base  of  motor 

VALVES  AND  VALVE  MECHANISM 
CAMSHAFT 

The  shafts  for  operating  the  cams,  irregularly  curved  lugs  which  operate 
the  valve  mechanisms,  are  known  as  camshafts.  The  material  generally  used 
is  open  hearth  or  drop-forged  steel;  the  bearings  are  of  bronze.  Camshafts 
are  drilled  to  reduce  weight. 

Two  methods  of  driving  or  rotating  the  camshaft  are  employed,  the  most 
common  being  by  means  of  gearing,  a  simple  spur  gear  such  as  shown  at  the 
left  of  Figure  56  being  employed  when  the  camshaft  is  horizontal,  or  parallel 
to  the  crank  shaft,  from  which  it  obtains  its  motion  at  half-speed. 

Operation  through  use  of  a  chain  drive  in  the  form  of  link  belts  over  toothed  pul- 
leys, is  the  second  method,  recently  come  into  some  favor  through  its  use  in  foreign 
engines. 

CAMS 

A  cam  is  a  lug  cast  integrally  on  the  camshaft  and  machined  to  a  form 
resembling  a  circle,  with  an  approximately  triangular  projection  at  one  point. 
It  is  this  projection  which  acts  on  the  valve  mechanism  as  the  shaft  rotates. 

Figures  57a  and  57b  show  cams  operating  on  overhead  valves,  the  former  acting  direct 
on  rocker  arms  and  the  latter  through  the  medium  of  a  tappet  rod.  Both  inlet  and  exhaust 
valves  are  operated  by  the  same  camshaft  in  general  practice,  although  many  exceptions  are 
made  in  engines  which  have  separate  camshafts  for  intake  and  exhaust  valves. 

VALVES 

In  almost  every  instance,  aviation  motors  have  valves  placed  in  the  head 
of  the  cylinder,  or  overhead  valves,  thereby  gaining  increased  power.  The 
valves  are  opened  by  the  mechanism  operated  by  the  camshaft  and  closed  by 
springs. 


Valves    and    Valve    Operation  67 

EXHAUST  VALVE 

Exhaust  valves  are  generally  made  of  tungsten  steel,  which  has  the 
necessary  high  resistance  to  the  heat  of  the  exploded  gases  which  pass  through 
the  exhaust.  The  disk  and  valve  seat  are  beveled  and  ground  so*  that  the 
valve  is  gas-tight  when  seated. 

Theoretically,  the  exhaust  valve  is  opened  only  during  one  of  the  four 
cycles  or  phases  of  the  engine's  operation,  that  is  on  the  upward  exhaust 
stroke.  In  practice,  however,  it  is  usually  opened  as  soon  as  the  piston  has 
moved  downward  through  about  seven-eighths  of  its  power  stroke,  or  j^-inch 
from  bottom  dead  center.  It  closes  exactly  at  the  finish  of  the  exhaust  stroke, 
or  in  some  cases  it  is  allowed  to  remain  open  until  the  piston  has  moved 
down  about  1-20-inch  on  its  intake  stroke,  so  that  all  exhaust  gas  has  a 
chance  to  escape. 

The  exhaust  ports  are  of  proper  dimensions,  varying  with  type  of  engine,  to  insure 
rapid  and  complete  expulsion  of  the  burnt  gas.  Exhaust  manifolds  are  seldom  used  as 
they  retard  this  expulsion,  but  short  pipes  are  common,  permitting  the  gas  to  exhaust 
into  the  open  air  but  carrying  it  away  from  the  aviator's  face,  and  reducing  the  danger 
from  fire. 

INLET  VALVE 

High  nickel  steel  or  cast  iron  are  the  materials  generally  used  for  inlet 
valves.  The  construction  of  valve  and  seat  is  identical  with  the  exhaust 
valves,  usually  beveled  and  always  ground  so  as  to  be  leak-proof  when  closed. 

The  inlet  valve  is  timed  to  open  when  the  piston  has  descended  about 
5^-inch  on  its  intake  stroke,  and  remains  open  until  the  piston  has  traveled 
about  ^-inch  up  on  the  compression  stroke.  This  permits  the  cylinder  to 
fill  with  gas,  the  downward  drive  of  the  piston  creating  a  suction  which  will 
remain  stronger  than  the  slight  upward  pressure  created  during  the  200th 
part  of  a  second  in  which  the  valve  remains  open  as  the  upward  compression 
stroke  begins. 

VALVE  OPERATING  MECHANISM 

Valve-in-the-head  motors  gain  flexibility  by  offering  no  resistance  to 
the  entrance  of  gas  into  the  combustion  chamber,  or  impediment  to  straight 
exhaustion.  But  the  valve  opening  mechanism  is  somewhat  more  compli- 
cated than  that  used  in  T-head  or  L-head  cylinders.  In  place  of  the  direct 
push  rod  action  from  the  cams  employed  by  the  latter,  the  valve  in  the  head 
motor  secures  its  opening  of  valves  by  the  system  of  rods  and  rocker  arms 
illustrated  in  two  forms,  respectively  in  Figures  57a  and  57b. 

In  Figure  57b,  the  camshaft  is  located  at  the  base  of  the  cylinders,  or  at 
the  crank  case,  being  rotated  by  bevel  gears  at  half  speed  from  the  crank 
shaft.  The  cam  pushes  up  the  tappet  rod,  raising  the  rocker  arm  at  one  end, 
which  pushes  down  the  valve  attached  to  the  other. 

Figure  57a  shows  a  form  of  construction  which  places  the  camshaft 
above  the  cylinders,  where  it  is  driven  by  bevel  pinion  and  gear  drive  by  a 
vertical  countershaft  from  the  crank  shaft.  This  form  of  construction  is 
being  adopted  by  many  American  aviation  engine  manufacturers,  since  it 
does  away  with  the  tappet  rods  and  simplifies  the  engine  construction. 

All  valves  are  closed  by  the  action  of  the  spring,  as  clearly  indicated  in 
the  drawings. 

VALVE  CLEARANCE 

Space  must  be  left  between  the  valve  stem  and  the  actuating  means,  the  amount 
of  clearance  depending  upon  the  design  of  the  engine.  The  clearance  is  indicated  as 
.020  inch  in  Figure  57a,  where  the  valve  stems  are  long;  in  the  Curtiss  0X2  engine  the 
clearance  is  .010  inch,  or  half,  the  variation  being  due  to  the  amount  of  valve  area  which 
becomes  .heated  and  expands  in  length  when  the  engine  is  running. 


68 


Practical    Aviation 


To  throttle 


Priming  tube  D-, 


float- 


Gasoline 
mlet 


Suffer f/y  f 

^ 

Secondary  well  f 


ChoHe 
Nozzle  6 

JetC 


locom 
Mixing  chamber  f  / 


ft>  combust/on  chombtr 


f/oot 
chamber 

\ 


4ir 
intake 


Compensator  A 


Figure  58  (left} — Sectional  view  of  carburetor  showing  details  of  the  compound  nozzle  and 

compensator 

Figure  59  (right) — The  duplex  carburetor  for  multiple  cylinder  engines 

CARBURETION 

Gasoline  will  not  burn  unless  it  is  mixed  with  air.  To  burn  with  great 
rapidity  and  heat,  or  to  "explode,"  as  required  by  the  internal  combustion 
engines  of  aviation,  the  air  must  be  in  correct  proportion  to  the  gasoline 
vapor;  these  proportions  range  from  18  to  20  parts  of  air  to  one  of  gasoline. 
The  vapor  is  produced  by  exposing  the  liquid  to  the  air,  generally  by  spray- 
ing into  a  mixing  chamber. 


PRINCIPLE  OF  THE  CARBURETOR 

The  device  in  which  the  vaporizing  of  gasoline  is  performed  is  termed 
a  carburetor.  There  are  numerous  types  used  on  airplanes,  but  the  standard 
construction  calls  for :  (a)  a  float  chamber  to  maintain  the  gasoline  at  a  con- 
stant level,  (b)  a  mixing  chamber  where  the  gasoline  is  sprayed  through  a 
nozzle  and  mixed  with  incoming  air.  In  the  form  of  vapor  it  is  then  drawn 
through  the  inlet  valve  into  the  cylinder  by  the  suction  of  the  down  stroke 
of  the  piston. 

The  throttle  valve,  or  butterfly,  generally  placed  above  the  spray  nozzle 
in  the  mixing  chamber,  regulates  the  amount  of  gas  entering  the  cylinder; 
this  valve  is  controlled  by  a  lever  near  the  pilot's  seat.  The  speed  of  the 
engine  increases  with  the  opening  of  this  throttle  and  decreases  accordingly 
as  it  is  closed. 

A  float  with  a  needle  valve  cuts  off  the  flow  of  gasoline  when  the  engine 
is  not  running. 


Carburetion  69 


CONSTRUCTION  OF  THE  CARBURETOR 

Figure  58  is  a  sectional  view  of  the  Zenith  carburetor,  selected  as  typical 
of  the  best  construction  and  widely  used  in  American  aviation  engines.  By 
a  compensator  and  compound  nozzle  principle,  this  carburetor  maintains  a 
constant  ratio  of  air  and  gasoline  at  the  most  efficient  combustion  mixture. 

The  advance  in  design  here  represented  is  the  elimination  of  variable  air 
valves  or  moving  parts.  The  construction  is  clearly  indicated  in  Figure  58. 
Gasoline  from  the  float  chamber  is  admitted  at  compensator  A  into  the  priming 
tube  D,  extending  into  the  secondary  well  E,  and  opening  at  the  priming  hole 
uncovered  by  the  action  of  the  butterfly  valve  F.  The  suction  at  the  priming  hole 
is  powerful  and  with  the  butterfly  partly  open  the  well  full  of  gasoline  is  drawn 
into  the  cylinders,  effectively  priming  the  motor. 

At  high  speeds  with  the  butterfly  opened  further,  the  priming  well 
ceases  to  operate  and  the  compound  nozzle  drains  the  well.  It  is  this  feature 
of  the  Zenith  carburetor  which  counteracts  the  defects  of  the  vaporization 
at  the  nozzle  of  the  conventional  carburetor  when  the  engine  is  operating 
at  low  speed. 

To  illustrate:  In  the  conventional  single  jet  carburetor  the  gasoline 
enters  by  suction  through  main  jet  B,  spraying  from  nozzle  G  in  the  path  of  air 
entering  through  the  inlet  at  the  lower  right  of  the  drawing,  Figure  58.  As  the 
speed  of  the  motor  increases,  the  air  flow  increases,  but  the  law  of  flow  of  liquid 
bodies  makes  the  flow  of  gasoline  from  the  jet  increase  faster,  giving  a  mixture 
which  increases  the  percentage  of  gasoline,  or  becomes  richer.  By  the  introduc- 
tion of  the  secondary  well  E,  the  gasoline  is  fed  through  the  compensator  A  and 
is  not  affected  by  the  suction,  since  the  well  is  open  to  atmospheric  pressure. 
The  flow  of  gasoline  is  therefore  made  constant  at  all  speeds,  it  being  obvious 
that  as  the  air  intake  increases  with  greater  speed,  the  mixture  becomes 
poorer.  The  combination  of  the  two  results  in  a  carburetor  giving  a  constant 
mixture. 

DUPLEX  CARBURETOR 

For  multiple  cylinder  aviation  engines,  arranged  in  V  form,  which  will 
be  discussed  later,  it  was  found  that  the  strong  cross  suction  in  the  inlet 
manifold  made  good  carburetion  difficult  with  a  single  carburetor.  The 
development  of  the  duplex  carburetor,  shown  in  Figure  59,  followed.  It 
provides  two  separate  mixing  chambers,  fed  by  a  common  float  chamber 
and  permitting  each  set  of  cylinders  a  separate  intake. 

MANIFOLDS 

As  the  gas  mixture  passes  upward  and  out  of  the  mixing  chamber  it 
reaches  the  cylinders  by  way  of  pipes  divided  into  branches  built  to  accom- 
modate the  model  of  motor,  and  termed  manifolds.  The  branches  of  the 
manifold  are  of  the  same  dimensions,  so  as  to  obtain  the  same  results  for 
all  cylinders  and  are  free  from  sharp  bends  or  obstructions  which  might 
retard  the  progress  of  the  gas  to  the  cylinders. 


70 


Practical    Aviation 


Practical  Aviation  71 


REVIEW  QUIZ 

Pistons,  Valves  and  Carburetors 

1.  Compare  the  average  life  of  a  motor  car  engine  and  an  aviation 

engine. 

2.  Describe  the  construction  of  the  piston. 

3.  What  is  the  purpose  of  the  piston  rings? 

4.  Name  two  types  of  piston  rings. 

5.  How  is  the  connecting  rod  constructed? 

6.  Give  two  additional  names  for  the  wrist  pin. 

7.  State   the   material   of   which   the   crank   shaft   is   constructed   and 

describe   its  features. 

8.  Are  propellers  always  mounted  on  the  crank  shaft  for  direct  drive? 

9.  Explain  the  construction  of  a  crank  case. 

10.  Give  two  methods  of  rotating  the  camshaft. 

11.  Describe  a  cam  and  how  it  operates  a  valve. 

12.  In  what  portion  of  the  engine  are  valves  usually  placed  and  how 

are  they  closed? 

13.  Why  is  the   exhaust  valve   generally  made  of  tungsten  steel  and 

how  is  it  made  gas-tight? 

14.  Give  the  essential  differences  in  valve  operating  mechanisms  which 

employ  tappet  rods  and  those  having  rocker  arms. 

15.  Why  is  valve  clearance  necessary? 

16.  State  what  change  is  necessary  in  gasoline  before  it  will  explode. 

17.  What  is  the  principle  of  the  carburetor? 

18-     Describe  in  detail  the  construction  and  operation  of  a  compound 
nozzle  carburetor. 

19.  How   many   float   chambers   has   the   duplex   carburetor   used    for 

V-motors  ? 

20.  Name  the  engine  part  through  which  the  gas  passes  to  the  com- 

bustion chamber. 


72  Practical    Aviation 


CHAPTER  ANALYSIS 

Ignition,  Cooling  and  Lubrication 
of  Engines 

IGNITION: 

(a)  Magneto. 

(b)  Distributor. 

(c)  Condenser. 

(d)  Circuit  Breaker. 

(e)  Spark  Plug. 

COOLING: 

(a)  Water  Cooling. 

(b)  Air  Cooling. 

LUBRICATION: 

(a)  Splash. 

(b)  Force-feed. 


CHAPTER  VIII 

Ignition,  Cooling  and  Lubrication  of  Engines 

Supplemental  to  the  description  and  definition  of  function  of  valves 
contained  in  the  previous  chapter,  the  student  will  find  a  knowledge  of  valve 
setting  and  valve  timing  of  value.  Instruction  in  these  two  operations,  as 
officially  given  for  the  Curtiss  engine,  follow: 

Valve  Setting — After  grinding  and  cleaning,  set  the  inlet  valves  at  0.010 
clearance  and  the  exhaust  valves  at  0.010  clearance.  This  setting  should  be 
done  on  each  cylinder  just  after  inlet  valve  has  closed.  If  the  stem  is 
indented  due  to  any  cause,  remove  the  valve  and  grind  the  stem  end  to  a 
flat  surface. 

Valve  Timing — After  setting  the  clearance,  turn  the  engine  in  the  direc- 
tion of  rotation  till  the  piston  of  No.  1  cylinder  is  1/16  inch  past  top  center. 
Then  turn  the  camshaft  in  its  direction  of  rotation  till  the  exhaust  valve  of 
No.  1  cylinder  has  just  closed.  Put  on  the  camshaft  gear,  being  sure  that 
the  keyway  of  the  gear  lines  up  with  the  key  in  the  camshaft. 

Thus  set  and  timed,  the  inlet  valves  will  open  12  degrees  past  top  center 
and  close  40  degrees  past  bottom  center;  the  exhaust  valves  will  open  45 
degrees  before  bottom  center  and  close  on  top  center. 

As  it  is  now  purposed  to  consider  ignition  and  its  relation  to  the  efficient 
operation  of  the  aviation  engine,  these  further  practical  suggestions  on  timing 
may  well  be  included. 

Magneto  Timing — Turn  the  engine  in  the  direction  of  rotation  till  the 
intake  valve  of  No.  1  cylinder  has  closed ;  then  turn  the  engine  in  the  same 
direction  till  the  piston  of  No.  1  cylinder  is  on  top  dead  center ;  then  turn  the 
motor  backward  till  the  piston  of  No.  1  cylinder  is  y2  inch  from  top  center. 
Turn  the  armature  of  the  magneto  in  the  direction  of  its  rotation  (it  is  the 
same  as  that  of  the  crank  shaft)  till  the  distributor  brush  is  on  No.  1  segment 
with  the  breaker  points  just  ready  to  open.  Put  on  the  magneto  gear,  using 
the  same  precaution  as  given  for  engaging  the  camshaft  gear.  This  should 
bring  the  firing-time  of  all  cylinders  to  30  degrees  before  top  center. 

The  spark  advance  lever  should  be  in  position  of  full  advance  during 
this  whole  operation.  The  gap  between  the  breaker  points  should  be  0.018 
inch  and  that  of  the  spark-plug  points  0.023  inch. 

73 


Practical    Aviation 


Ftire  washer 
Porce/ajn 
Steel  body. 
Porcelain  s/e eve 
ft tc fa J  point 

Figure  6 2-  a 


spring  washer 
frpansion  and 
•contraction  spring 


Distributor 
/ 


**Jlsbesfo5  pocking 
^Standard  thread 


Armature- 


Inter  adjust 


'Insulated  contact 


figure  62-b 


Figure  61 — A  high 
tension  magneto 


Figure  62a — Construction  of  spark  plug 
Figure  62b — General  view  of  spark  plug 


Figure  63 — Construction 
of  the  magneto 


IGNITION 

To  set  afire  the  compressed  gas  mixture  in  the  cylinder  at  the  proper 
time  an  electric  spark  is  produced  in  the  combustion  chamber,  through  the 
medium  of  a  spark  plug,  the  points  of  which  offer  a  break  in  the  ignition 
circuit,  causing  the  current  to  jump  the  gap  and  spark.  The  essentials  of  an 
ignition  system  for  aviation  engines  are,  (a)  a  method  of  producing  the  cur- 
rent, (b)  timing  apparatus  to  regulate  the  sparking  at  the  proper  instant  in 
each  cylinder,  (c)  wiring  and  auxiliary  devices  to  carry  the  generated  current 
to  the  spark  plug  in  the  cylinder. 

MAGNETO 

Aviation  motors  are  equipped  with  high-tension  magnetos,  i.e.,  those  with  a  second- 
ary winding  of  fine  copper  wire  over  the  primary  winding,  as  distinguished  from  the 
low-tension  type  with  primary  coil  only.  In  the  coarse  wire  winding,  or  primary  (on 
top  of  which  is  the  secondary  winding  of  fine  wire)  a  low-tension  current  is  generated 
as  the  armature  revolves  between  the  ends  of  the  magnets.  This  low-tension  current 
then  flows  to  the  circuit  breaker,  where  it  is  broken  by  the  points  operated  by  a  cam. 
The  current  then  goes  to  a  condenser  for  storage  until  the  points  again  close.  Break- 
ing the  current  creates  a  high-tension  current  which  flows  to  the  distributor  and  spark 
plugs. 

Figure  61  shows  the  Berling  high-tension  magneto,  used  on  Curtiss  engines  and 
one  of  the  best  of  the  representative  types;  Figure  63  shows  the  construction. 

DISTRIBUTOR 

The  distributor  is  the  device  wherein  both  the  primary  and  secondary  currents  gen- 
erated by  the  magneto  are  collected  by  a  brush  and  distributed  to  the  proper  cylinder 
at  the  proper  time. 

CONDENSER 

Absorption  of  the  self-induced  current  of  the  primary  winding,  thereby  preventing 
it  opposing  the  rapid  fall  of  the  primary  current,  is  the  function  of  the  condenser. 

CIRCUIT  BREAKER 

This  device  keeps  the  circuit  closed  except  at  the  time  of  sparking. 
SPARK  PLUG 

This  device  consists  of  an  insulating  member  screwed  into  the  cylinder  and  carrying 
the  terminal  electrodes  across  which  the  spark  for  ignition  jumps.  The  secondary  wire  from 
the  coil  is  attached  to  a  terminal  at  the  top  of  the  central  electrode.  Details  of  construction 
of  the  spark  plug  are  shown  in  Figures  62a  and  62b. 

Spark  plugs  are  screwed  into  the  combustion  chamber  directly  in  the  path  of  the  incoming  gases  from 
the  carburetor.  On  most  aviation  engines  a  double  set  of  plugs  is  used,  two  to  a  cylinder,  igniting  the 
mixture  at  two  different  points  and  thereby  gaining  twenty-five  per  cent  motor  power  at  high  speed. 


Water    and    Air    Cooling 


75 


Water  outlet 


Cooling 
-"flange 


Figure  64 — Radiator  at  front 
of  fuselage 


Figure  65a — Water-cooled 
cylinder 


Figure  6Sb — Air-cooled 
cylinder 


COOLING 

The  intense  heat  of  the  explosions  in  engine  cylinders  would  heat  the 
metal  portions  to  a  point  where  the  lubricating  oil  would  be  burned  and 
become  useless  and  the  piston  rings  expand  and  bind  in  the  cylinder  walls, 
if  a  means  of  cooling  was  not  provided.  There  are  two  general  systems  of 
cooling:  (a)  water  cooling;  (b)  air  cooling. 

WATER  COOLING 

This  system  consists  of  a  circulation  of  water  through  jackets  which 
surround  the  heated  portion  of  the  cylinder  wall ;  a  radiator,  constructed  of 
thin  metal  tubes  with  a  large  exposed  surface  area,  wherein  the  water  is 
cooled;  and  a  means  of  keeping  the  water  in  circulation  from  the  cylinder 
jackets  to  the  radiator,  and  back  again  through  the  system. 

Figure  64  illustrates  one  form  of  radiator,  constructed  at  the  front  of 
the  fuselage  with  provision  for  the  propeller  hub. 

Figure  65a  is  a  view,  partly  in  section,  of  a  cylinder  with  water  jacket  cast 
integral. 

The  water  is  circulated  either  by  a  pump  which  is  gear-driven  from  the 
motor,  or  it  is  automatically  circulated  by  the  thermo-syphon  principle,  which 
utilizes  the  tendency  of  heated  water  to  rise. 

When  the  airplane  is  at  its  angle  of  steepest  climb  maximum  heating  of  the  motor 
occurs.  For  this  reason,  radiators  are  constructed  so  the  cells  are  not  horizontal,  but 
parallel  to  a  tangent  of  the  mean  trajectory  of  climb. 

AIR  COOLING 

Cooling  flanges,  or  metal  fins,  are  radiated  from  the  cylinder  walls  in 
the  air-cooled  type  of  engine,  to  absorb  the  heat  of  the  explosions  and  diffuse 
it  in  the  rush  of  air.  The  cylinders  are  placed  directly  in  the  path  of  the 
propeller  slip  stream  and  often  a  powerful  fan  is  used  to  increase  the  rate 
and  degree  of  cooling. 

Figure  65b  shows  an  air-cooled  cylinder,  partly  in  section. 

The  principal  advantage  of  air  cooling  is  reduction  of  weight  through  the  elimina- 
tion of  the  various  parts  of  the  water  cooling  system.  Rotary  radial  cylinder  types  have 
proved  practical  with  air  cooling,  but  it  is  generally  conceded  that  the  water-cooled 
motor  is  best  for  long  flights. 


76 


Practical    Aviation 


Oil  over  flow*-. 


v. 


Oil  rings  on  piston 
circulate  oil  into  holtoir» 
tirr/st  pin. 

Oil  overflow  lubricates 
gears,  excess  oil  flowing  ( 
down  through  magneto, 
gear  housing  into  samp: 

Individual  oil  pipe  to   ; 
each  cy/inderautomti 
tically  injecting  oil—' 
to  pistons  as  each 
one  passes  oil  port 


Relief  valve  through  Nhtch  / 
excess  oi  If  lorn  bac/r  into  sump. 


Cam  shaft  oiling  through 
hanapump 


Jil  ftoHf/ng  from  coo/ing  resevo/rs 
info  main  oil  pipe. 

Leads  to  bottom  of  each 
main  bearing. 


Mo/n  oi/  p/pe 


-  Hoi/on  cran/t  pin  for 
oiling  conn,  rod  bearing 
Plates 
Sump  and  resevo/r  of  oil 

Oil\  strainer 


Figure  66 — A  modern  oiling  system  for  aviation  engines 

LUBRICATION 

The  necessity  for  providing  some  means  of  preventing  excessive  friction 
between  swiftly  moving  parts  is  due  to  the  heating  which  would  result  if  a 
lubricant  was  not  applied  between  them.  The  temperature  of  the  aviation 
engine  as  a  whole  is  an  additional  reason  for  insuring  proper  oiling  of  parts. 

Two  types  of  motor  lubrication  are  in  use: 

(a)  Splash   lubrication — Oil   is   held   in   the   sump,    or   reservoir  at   the 
bottom  of  the  crank  case,  and  splashed  on  the  moving  parts  by  the  revolu- 
tions of  the  crank  shaft. 

(b)  Force-feed — Positive  mechanical  means  deliver  the  oil  under  pres- 
sure to  the  various  working  parts  of  the  engine. 

Owing  to  the  evolutions  of  the  airplane  in  flight,  lubricating  systems  have  been 
elaborated  to  deliver  oil  as  needed  to  all  working  parts  and  to  eliminate  the  possibility 
of  flooding  cylinders. 

FORCE-FEED  LUBRICATION 

Figure  66  gives  a  clear  illustration  of  a  modern  oiling  system  for  aviation  engines; 
in  this  instance,  the  Hall-Scott  engine,  representative  of  the  best  practice  in  lubrication. 

The  crank  shaft,  connecting  rods  and  all  other  parts  within  the  crank  case  and 
cylinders  are  lubricated  directly  or  indirectly  by  a  forced-feed  oiling  system.  The  cylin- 
der walls  and  wrist-pins  are  lubricated  by  oil  spray  thrown  from  the  lower  end  of  the 
connecting  rod  bearings.  The  oil  is  drawn  from  the  strainer  located  at  the  lowest  por- 
tion of  the  crank  case,  forced  around  the  main  intake  manifold  jacket.  From  here  it  is 
circulated  to  the  main  distributing  pipe  located  along  the  lower  left  hand  side  of  the 
upper  portion  of  the  crank  case.  The  oil  is  then  forced  directly  to  the  lower  side  of  the 
crank  shaft,  through  holes  drilled  in  each  main  bearing  cup.  Leakage  from  these  main 
bearings  is  caught  in  scuppers  placed  upon  the  cheeks  of  the  crank  shaft,  furnishing  oil 
under  pressure  to  the  connecting  rod  bearings. 

A  bi-pass  located  at  the  front  end  of  the  distributing  oil  pipe  can  be  regulated  to 
lessen  or  raise  the  pressure.  By  screwing  the  valve  in,  the  pressure  will  raise  and  more 
oil  will  be  forced  to  the  bearings.  By  unscrewing,  pressure  is  reduced  and  less  oil  is  fed. 

Independent  of  the  above-mentioned  system,  a  small,  directly  driven  rotary  oiler 
feeds  oil  to  the  base  of  each  individual  cylinder.  The  supply  of  oil  is  furnished  by  the 
main  oil  pump  located  in  the  lower  half  of  the  crank  case.  A  small  sight-feed  regula- 
tor controls  the  supply  of  oil  from  this  oiler.  This  instrument  is  placed  higher  than  the 
auxiliary  oil  distributor  itself  to  enable  the  oil  to  drain  by  gravity  feed  to  the  oiler. 

The  oil  sump  plug  is  located  at  the  lowest  point  of  the  crank  case.  This  is  a  trap 
for  dirt,  water  and  sediment  and  is  removed  by  unscrewing.  Oil  is  furnished  mechanic- 
ally to  the  camshaft  housing  under  pressure  through  a  small  tube  leading  from  the 
main  distributing  pipe  at  the  propeller  end  of  the  engine  directly  into  the  end  of  the 
camshaft  housing.  The  opposite  end  of  this  housing  is  amply  relieved  to  allow  the 
oil  to  rapidly  flow  down  upon  camshaft,  magneto,  pinion-shaft,  and  crank  shaft  gears, 
after  which  it  returns  to  the  lower  crank  case.  An  outside  overflow  pipe  is  also  pro- 
vided to  carry  away  the  surplus  oil. 


Practical    Aviation  77 


REVIEW  QUIZ 

Ignition,  Cooling  and  Lubrication  of  Engines 

1.  What  valve  in  the  first  cylinder  should  be  closed  as  the  initial  step 

in  magneto  timing? 

2.  Explain  the  next  steps  up  to  the  time  when  the  magneto  gear  is 

put  on. 

3.  What  should  be  the  position  of  the  spark  lever  during  the  timing 

operation? 

4.  Give  the  dimensions  of  the  gap  between  breaker  points.  Spark  plug 

points. 

5.  Why  is  ignition  required  in  aviation  motors? 

6.  What  comprises  an  ignition  system? 

7.  State  the  principal  construction  difference  between  a  high-tension 

magneto  and  a  low-tension  magneto. 

8.  Briefly  explain  how  the  high-tension  magneto  generates  low-tension 

current  and  changes  it  to  high-tension  current. 

9.  What  purpose  is  served  by  the  distributor? 

10.  Define  the  functions  of  the  condenser  and  the  circuit  breaker. 

11.  Describe  the  spark  plug  and  give  the  reason  why  aviation  engines 

usually  employ  a  double  set. 

12.  Why  is  provision  for  cooling  an  engine  required? 

13.  Name  the  principal  parts  of  a  water  cooling  system  and  explain 

how  circulation  is  gained. 

14.  What   differences   in   construction  of  cylinder  walls  are  made  for 

air  cooling? 

15.  State  the  principal  advantage  gained  by  air  cooling. 

16.  In  what  way  is  water  cooling  superior? 

17.  Give  two  reasons  why  lubrication  of  engines  is  necessary. 

18.  Name  the   two  types   of  motor  lubrication  and   explain  how  they 

differ. 

19.  How  are  parts  within  crank  case  and  cylinders  oiled  by  a  force- 

feed  system? 

20.  How  are  dirt,  water  and  sediment  removed? 


78  Practical    Aviation 


CHAPTER  ANALYSIS 

Types  of  Motors,  Operation  and  Care  of  Engines 

BORE  AND  STROKE  RATIO: 

(a)  Long  Stroke. 

(b)  Short  Stroke. 

V-TYPE    MOTORS: 

(a)  8-Cylinder. 

(b)  12-Cylinder. 

(c)  The  Liberty  Motor. 

ROTARY    ENGINES: 

(a)  Elements  of  Design. 

(b)  The  Gnome  Engine. 

STARTING  THE  ENGINE: 

(a)  Preparatory. 

(b)  Swinging  the  Propeller. 

(c)  Signals. 

(d)  Self-Starters. 

FUEL  CONSERVATION  IN  FLIGHT: 

(a)  Speed. 

(b)  Altitude. 

CARE  OF  ENGINES: 

(a)  General  Rules. 

(b)  The  Trouble  Chart. 


CHAPTER  IX 


Types  of  Motors,  Operation  and  Care  of  Engines 


Fundamentals  of  the  theory  of  operation  and  construction  of  aviation 
engine  parts  have  been  covered  in  sufficient  detail  for  the  student  aviator 
in  previous  chapters.  It  but  remains  to  consider  as  types,  a  few  of  the  more 
advanced  engines,  and  the  balance  of  motor  instruction  may  be  safely  left  to 
shop  practice,  where  actual  assembly  should  be  undertaken.  The  engineering 
factors  which  enter  into  the  design  of  motors  can  be  made  a  supplementary 
study,  if  desired,  but  the  air  pilot  of  wartime  is  not  required  to  have  the 
full  mathematical  knowledge  of  the  laboratory  expert,  acquired  only  by 
painstaking  study  and  entire  concentration  on  that  particular  phase  of 
aviation. 

Due  to  the  ever-changing  refinements  of  design  the  aim  has  been  to 
present  the  various  parts  as  representative  of  the  best  practice,  describing  the 
function  and  operation  and,  in  a  brief  manner,  the  construction.  In  this  way 
the  aviator  learns  the  fundamentals,  so  that  he  is  able  to  instantly  com- 
prehend the  operation  of  any  advanced  design  which  he  may  later 
encounter. 

A  word  may  be  said  on  bore  and  stroke  ratio.  While  nothing  fixed, 
definite  and  exact  may  be  stated  on  the  proper  proportion  of  bore  to  stroke, 
it  is  clear  that  an  engine  with  a  short  stroke  will  run  at  high  speed  smoothly 
but  is  of  poor  efficiency  at  low  speeds.  When  the  stroke  is  much  longer  than 
the  diameter  of  the  cylinder  bore,  the  reverse  is  true.  A  bore  of  5  inches  and 
a  stroke  of  8  inches  is  considered  a  long  stroke  ratio,  4"  x  5"  a  short  stroke. 
Since  both  ratios  have  their  disadvantages  there  is  no  agreement  of  opinion 
among  designers ;  thus  in  seven  representative  types  of  aviation  motors  the 
following  ratios  are  found:  4x5,  4x5^,  4x6,  4^x5,  4^x5,  5x6*/2,  5x7.  Among 
foreign  motors  the  average  is  a  stroke  1.2  times  the  bore  dimension.  The 
general  trend  in  motor  design  is  steadily  leaning  toward  the  short  stroke,  or 
high  speed  engine,  and  recent  calculations  make  it  appear  that  the  practice 
of  restraining  piston  speed  to  1,000  feet  per  minute  will  be  abandoned. 

A  few  representative  types  of  multi-cylinder  engines  will  now  be  briefly 
considered. 

79 


Practical    Aviation 


.5  "a 


C5    5£ 

s^'-S 
o  s 


i* 


V-Type    Motors 


81 


Valve  rod 


Water 
pump 


Figure  67a — Part  section  view  of  ^-cylinder 
J '-motor 


Figure  67 b — Part  section  view  of  same  mo- 
tor from  the  front 


V-TYPE    MOTORS 

The  salient  advantages  of  increasing  the  number  of  cylinders  in  aviation 
engines  are,  briefly,  high  speed  with  decreased  vibration,  flexibility  and  quick 
operation,  overlapping  power  strokes  and  lighter  reciprocating  parts.  The 
addition  of  more  cylinders  to  the  vertical  type  of  motor  is  impracticable  be- 
cause this  would  require  a  length  too  great  for  the  fuselage  and  a  much 
stronger  and  heavier  crank  shaft ;  the  best  solution  is  therefore  found  in  two 
sets  of  cylinders  inclined  inward  at  an  angle,  thus  producing  a  motor  of  same 
length  but  increased  power,  or  the  V-type  motor. 

8-CYLINDER    V-MOTOR 

The  standard  Curtiss  engine  is  shown  in  part  section  in  Figures  67a  and  67b. 
It  will  be  noticed  that  the  length  of  the  motor  and  crank  shaft  is  practically 
the  same  as  in  a  4-cylinder  engine,  and  the  additio'ns  are  merely  another  set  of 
cylinders  and  connecting  rods. 

In  this  engine  the  cylinders  are  set  at  an  angle  of  90  degrees,  or  one-half 
the  firing  distance  of  the  4-cylinder  engine.  That  is,  in  this  V-type  motor  the 
power  impulses  occur  every  90  degrees  instead  of  180  degrees.  In  the  Curtiss 
OX,  or  90  horsepower  engine,  widely  used  in  training  machines,  the  cylinders 
have  4-inch  bore  and  5-inch  stroke,  is  normally  run  at  1400  revolutions  per 
minute  (r.  p.  m.)  and  weighs  390  pounds  complete. 

The  main  difference  between  the  8-cylinder  V-motor  and  the  4-cylinder  vertical,  is 
the  arrangement  of  the  connecting  rod;  it  is  common  practice  to  have  two  rods  attached 
to  the  same  crank  throw.  This  is  accomplished,  (a)  by  staggering  the  cylinders  and 
having  the  connecting  rods  attached  side  by  side  to  the  same  crankpin,  or  (b)  the  lower 
end  of  the  connecting  rod  is  forked  just  above  the  crank  shaft  bearing,  and  the  rod  from 
the  cylinder  opposite  connected  to  the  crank  shaft  bushing  (at  a  right  angle)  between 
the  fork. 

The  firing  order  is  generally  the  same  as  in  a  4-cylinder  motor,  except  that  the 
explosions  occur  alternately  in  each  set  of  cylinders. 

12-CYLINDER   V-MOTOR 

The  development  of  the  multi-cylinder  engine  to  12  cylinders  responded 
to  the  demand  for  more  power.  In  y  form,  it  possesses  the  same  advantages 
of  arrangement  and  lightness  of  weight  as  the  8-cylinder,  and  obviously 
reduces  vibration  still  further.  That  is,  where  the  8-cylinder  engine  has  four 
power  impulses  per  revolution,  the  12-cylinder  motor  gives  six  explosions 
per  revolution. 

The  usual  practice  has  been  to  set  the  cylinders  at  a  60  degree  angle,  but  the  latest 
design  favors  an  angle  of  45  degrees. 


82 


Practical    Aviation 


Figure  68 — Cross  section  of  a  \2-cyl- 

inder  engine,  illustrating  many 

features  of  advanced  design 


THE  LIBERTY  MOTOR 

Details  of  the  general  construction  of  the  Liberty  motor  have  been  given  in  an 
authorized  statement  issued  by  the  War  Department,  extracts  from  which  follow: 

CYLINDERS 

The  cylinders  follow  the  practice  used  in  the  German  Mercedes,  English  Rolls 
Royce,  French  Lorraine  Dietrich  and  Italian  Isotta  Fraschini.  The  cylinders  are  made 
of  steel  inner  shells,  surrounded  by  pressed  steel  water  jackets.  (This  construction  is 
clearly  shown  in  Figure  68,  a  cross  section  of  a  Renault  engine.)  The  valve  cages  are 
drop-forged,  welded  into  the  cylinder  head;  the  principal  departure  from  European 
practice  is  in  the  location  of  the  holding  down  flange,  which  is  several  inches  above  the 
mouth  of  the  cylinder. 

CAMSHAFT  AND  VALVE  MECHANISM 

The  design  of  the  cam  and  valve  mechanism  is  based  on  the  Mercedes,  but  im- 
proved for  automatic  lubrication  without  wasting  oil.  Figure  68  illustrates  a^good  ex- 
ample of  the  type,  which  has  been  described  in  detail  on  page  66.  The  camshaft  drive 
is  of  the  Hall-Scott  type. 


ANGLE  BETWEEN  CYLINDERS 

The  included  angle  between  cylinders  of  the  Liberty  motor  is  forty-five  degrees, 
or  similar  to  the  illustration  Figure  68. 

The  general  practice  in  12-cylinder  engines  has  been  to  set  the  cylinders  at  sixty 
degrees,  but  by  lessening  the  angle  each  row  of  cylinders  is  brought  nearer  the  vertical 
and  closer  together,  saving  width  and  head  resistance,  reducing  vibration  and  giving 
greater  strength  to  the  crank  case. 


The    Liberty    Motor  83 


PISTONS  AND  CONNECTING  RODS 

Hall-Scott  design  has  been  followed  for  Liberty  motor  pistons;  these  are  similar 
in  type  to  those  shown  in  the  drawing  on  the  opposite  page.  The  connecting  rods  are 
of  the  straddle  or  forked  type,  the  fork  being  just  above  the  bearing  at  the  crank  shaft  end. 


CRANK  SHAFT  AND  CRANK  CASE 

Standard  12-cylinder  engine  practice  is  followed,  except  as  to  modifications  in  the 
oiling  system. 


IGNITION 

A  specially  designed  Delco  ignition  system  is  used. 

LUBRICATION 

The  first  system  of  lubrication  followed  the  German  practice  of  using  one  pump  to 
keep  the  crank  case  empty,  delivering  into  an  outside  reservoir,  and  another  pump  to 
force  oil  under  pressure  to  the  main  crank  shaft  bearings.  This  lubrication  system  also 
followed  the  German  practice  in  allowing  the  overflow  in  the  main  bearings  to  travel 
out  the  face  of  the  crank  cheeks  to  a  scupper,  which  collected  this  excess  for  crankpin 
lubrication.  This  is  very  economical  in  the  use  of  oil  and  is  still  the  standard  German 
practice. 

The  present  system  is  similar  to  the  first  practice,  except  that  the  oil,  while  under 
pressure,  is  not  only  fed  to  main  bearings,  but  through  holes  inside  of  crank  cheeks  to 
crankpins,  instead  of  feeding  these  crankpins  through  scuppers.  The  difference  between 
the  two  oiling  systems  consists  of  carrying  oil  for  the  crankpins  through  a  hole  inside 
the  crank  cheek,  instead  of  up  the  outside  face  of  the  crank  cheek. 

CARBURETOR 

The  carburetor  is  a  Zenith  development.  The  compound  nozzle  principle  of  the 
Zenith  and  the  constructional  details  are  described  on  pages  68  and  69. 

BORE  AND  STROKE 

The  bore  and  stroke  of  the  Liberty  engine  is  5x7  inches. 

The  first  Liberty  motor  was  an  eight-cylinder  model,  delivered  to  the  Bureau  of  Standards  July  3,  1917. 
The  eight-cylinder  model,  however,  was  never  put  into  production,  as  advices  from  France  indicated  that 
demands  for  increased  power  would  make  the  eight-cylinder  model  obsolete  before  it  could  be  produced. 


84 


Practical    Aviation 


I 


Rotary     Engines 


85 


Figure  69a — General  view  of  nine-cylinder 
rotary  engine 


Figure  69b — Section  view  of  rotary 
engine  cylinder  and  crank  case 


ROTARY    ENGINES 

The  principal  claim  advocated  for  rotary  motors  is  that  the  design  makes 
for  light  weight.  It  has  been  observed,  however,  that  the  rotating  feature 
has  little  to  do  with  this  advantage,  for  the  weight  would  not  be  perceptibly 
increased  if  the  cylinders  were  stationary  and  the  crank  shaft  revolved.  Set- 
ting cylinders  radially  from  a  crank  case  of  a  size  not  much  larger  than  that 
which  one  cylinder  would  require  is  an  obvious  weight  saving.  The  absence 
of  reciprocating  parts  aids  smooth  running  and  the  full  practicability  of  air 
cooling  is  an  added  advantage.  The  head  resistance  is  a  disadvantage,  and 
the  loss  of  power  (estimated  at  7  per  cent)  in  driving  the  cylinders  around 
the  shaft,  and  the  difficulty  of  securing  high  compression,  further  handicap 
this  design. 

GNOME   ENGINE 

The  Figures  69a  and  69b  show  the  famous  Gnome  engine  with  nine  radial 
cylinders.  The  explosions  occur  in  each  alternate  cylinder  as  the  engine  revolves, 
the  odd  number  thus  securing  a  uniform  period  of  explosion.  The  cylinders, 
the  construction  of  which  is  shown  in  section  in  Figure  69b,  are  machined  from 
solid  6-inch  steel  bars,  11  inches  in  length,  weighing  less  than  100  pounds. 

The  operation  of  the  engine  is  as  follows : 

Vaporized  gasoline  is  forced  into  the  crank  case  through  the  jet  F  (Figure  69b)  entering 
the  cylinder  through  the  holes  A,  B,  when  the  piston  is  at  the  lowest  point.  As  the  piston 
ascends  it  covers  the  port  and  the  gas  is  compressed  and  fired  in  the  usual  manner.  The 
large  valve  in  the  cylinder  head  is  the  exhaust,  operated  by  a  cam  and  rod.  Lubricating  oil 
enters  at  C  on  the  stationary  crank  shaft,  passing  to  the  stationary  crankpin  D  and  flooding 
the  bearings  E.  A  portion  of  the  oil  which  lubricates  the  crankpins  is  thrown  by  centrifugal 
force  through  the  connecting  rod  tubes  and  in  the  same  way  oils  the^  piston  pins  and  cylin- 
ders. Additional  lubrication  of  the  cylinders  is  secured  by  oil  which  is  thrown  through 
crank  case  holes. 

In  Figure  69a  the  engine  is  shown  with  the  crank  case  cover  removed,  reveal- 
ing- the  cams  and  gears.  One  of  the  nine  holes  in  the  crankpin,  through  which  oil 
is  fed  to  the  nine  cams,  is  indicated  at  A.  The  cam  rollers,  one  of  which  is  shown 
at  B,  carry  oil  over  the  surface  of  the  cam,  surplus  oil  feeding  through  the  guides 
C  of  the  valve  rods,  through  the  ball  joint  D  and  hollow  rod  E  to  the  pin  F.  A 
groove  on  the  valve  lever  carries  the  lubrication  to  the  lever  bearing  G. 

Other  aviation  engines  of  the  rotary  type  include  the  Anzani,  Le  Rhone  and  Clerget,  constructed  with 
varying  number  of  cylinders  up  to  fourteen. 


86 


Practical    Aviation 


Figure  70 — The  proper  method  of  swinging  the  propeller 


STARTING  THE  ENGINE 
PREPARATORY 

The  ground  selected  should  be  firm  so  that  the  foot  will  not  slip  when  the  propeller 
is  swung.  The  blocks  are  then  placed  in  front  of  the  wheels  with  the  cords  laid  toward 
the  wing  tips.  A  mechanician  takes  his  place  at  each  wing  tip,  grasping  the  bottom  of 
the  outer  strut  to  steady  the  airplane  when  the  engine  is  running;  they  pull  the  blocks 
away  when  the  pilot  signals  he  is  ready  to  start.  Two  or  more  mechanicians  take  their 
places  at  the  tail  end  of  the  fuselage  to  hold  it  down  while  the  engine  is  running. 

SWITCH  OFF 

The  ignition  switch  must  be  in  the  "off"  position  before  any  attempt  is  made  to 
swing  the  propeller.  Many  fatal  accidents  have  resulted  from  carelessness  on  this  point. 

With  engines  of  the  rotary  type  it  is  often  necessary  to  prime  the  cylinders  by 
squirting  gasoline  through  each  exhaust  valve.  Two  things  are  to  be  remembered  in 
this  connection:  The  squirt  can  must  be  clean  and  the  ignition  switch  off. 

GASOLINE  ON  AND  AIR  CLOSED 

The  pilot  ascertains  that  the  gasoline  is  on  and  the  air  intake  almost  closed,  so 
the  mixture  may  be  rich  for  the  first  few  explosions. 

ROTATION  OF  PROPELLER 

The  propeller  is  swung  with  the  ignition  switch  off  to  fill  the  cylinders  with  gas. 
CONTACT 

The  mechanician  calls  "contact"  at  this  juncture,  whereupon  the  pilot  throws  the 
ignition  switch  on,  and  replies  "contact." 

SWINGING  PROPELLER 

The  propeller  is  grasped  as  shown  in  Figure  70.  Note  particularly  the  position  of 
the  feet,  shown  in  plain  view  at  the  lower  right  of  the  drawing.  One  good  downward 
swing  of  the  propeller  is  made  and  the  mechanician  immediately  stands  clear.  If  the 
engine  fails  to  start  the  mechanician  calls  for  "switch  off"  and  repeats  the  same  operation. 

Once  the  propeller  has  been  given  its  downward  swing,  the  mechanician  must  stand 
clear  immediately,  as  the  possibility  of  a  backfire  from  the  engine  is  great  and  the  back- 
ward swing  of  the  propeller  may  result  in  a  fatal  accident.  The  illustration,  Figure  70, 
should  be  carefully  studied,  with  particular  reference  to  keeping  the  feet  apart  and  in  a 
position  where  the  body  will  naturally  swing  away  with  the  downward  pull. 


Starting    the    Motor    and    Fuel    Conservation  87 

____^ _ 1 

SIGNALS 

The   following   procedure   is   standard  with   the   Royal    Flying   Corps. 

1.  The    pilot   ascertains    from    the    rigger    and    the    mechanician    that   everything   is    correct,    immediately 
after  entering   the   machine. 

2.  Mechanician — "Switch   off?" 

3.  Pilot— "Switch  off." 

4.  Mechanician — '"Gas   on — air  closed?" 

5.  Pilot — "Gas  on — air  closed." 

6.  The  mechanician   rotates  the   propeller   to   fill   the   cylinders   with   gas. 

7.  Mechanician — "Contact?" 

8.  Pilot — "Contact." 

9.  The  Mechanician  swings  the   propeller  and  stands  clear.      The   engine   runs  for  a  few  minutes   until 
the  pilot  is  assured  that  the   motor  is  in   good   working   order. 

10.  Pilot  waves  hand  from  side  to   side. 

11.  Mechanicians  pull  blocks  away  from  wheels. 

12.  Pilot  looks  at  aviation  mechanician  or  senior  non-com,  who  ascertains  if  all  is  clear  ahead  and  above 
for  the  ascent.     He  indicates  all  clear  by  saluting. 

13.  Pilot  waves  hand  in  fore  and  aft  direction.     This  is  the  signal  to  start  and  all  stand  clear  instantly, 
the  mechanicians  at  the  tail  letting  go  immediately. 

SELF  STARTERS 

There  are  two  methods  of  cranking  aviation  engines  by  starting  systems 
employing  compressed  air.  One  turns  the  crank  shaft  by  means  of  an  air 
motor  and  the  other  admits  compressed  air  to  the  cylinders,  forcing  the  piston 
down  by  pressure  and  thus  turning  the  motor  over.  In  the  latter  case,  air 
for  the  system  is  supplied  to  a  reservoir  by  an  air  pump  driven  by  the  engine 
and,  when  needed,  enters  the  top  of  the  cylinders  in  their  proper  firing  order 
by  means  of  check  valves  which  open  inward  only  and  close  by  explosive 
pressure  once  the  engine  is  running. 

Developments  of  the  electric  starters  familiar  to  all  automobilists  are 
also  being  employed  on  aviation  engines.  These  are  of  the  storage  battery 
type  with  the  current  generated  by  the  engine  when  running  and  stored  for 
use  until  needed.  The  motor  in  this  instance  is  turned  over  when  electrical 
communication  is  made  between  the  storage  battery  and  the  motor-generator 
unit,  which  then  acts  as  a  motor  and  turns  the  engine  over  by  means  of 
gearing  to  the  crank  shaft. 

FUEL  CONSERVATION   IN   FLIGHT 

A  final  word  may  well  be  added  before  turning  to  the  aspects  of  actual 
flight.  When  flying,  the  pilot  must  bear  in  mind  that  the  maximum  speed  of 
the  plane  is  not  its  most  efficient  flight  speed,  and  driving  the  machine  at 
full  power  must  not  become  an  habitual  practice.  The  aviator  soon  learns  by 
experience  the  range  of  speed  of  his  machine  and  upon  this  knowledge  must 
base  his  calculations  for  long  flights,  so  his  fuel  may  be  properly  conserved 
for  the  task  in  hand. 

To  illustrate,  a  given  motor  may  be  assumed  to  develop  90  H.P.  at 
1300  r.p.m.  and  consume  1-10  gal.  of  gasoline  per  horsepower  hour,  or  9  gal- 
lons per  hour.  If  the  gasoline  tank  holds  18  gallons  and  the  speed  at 
1300  r.p.m.  is  80  miles  per  hour,  the  duration  of  flight  will  be  2  hours,  or  160 
miles.  If  then,  the  number  of  revolutions  is  reduced  to  a  point  where  the 
fuel  consumption  is  one-half  (at  a  speed,  say,  of  60  m.p.h.)  the  fuel  will  last 
twice  as  long,  or  4  hours,  and  the  distance  covered  will  be 

60  m.p.h.  x  4  hrs.  =  240  miles 
as  against  160  miles  at  the  greater  speed. 

When  flying  at  high  altitudes,  10,000  feet  or  more,  motor  troubles  increase.  The 
explosive  mixture  changes  in  character,  due  to  the  decreased  density  of  the  air  supplied 
to  the  carburetor.  Lessened  supply  of  air  results  in  increased  richness  of  mixture  and, 
disregarding  factors  of  motor  design  and  construction,  the  amount  of  power  obtained 
will  vary  with  the  changes  in  the  proportions  of  the  gasoline  vapor.  Increased  air  in  the 
mixture  means  fuel  economy,  but  lessened  power.  With  a  rich  mixture,  on  the  other 
hand,  though  the  power  curve  rises,  the  motor  and  its  parts  overheat,  delicate  adjust- 
ments are  thrown  out  and  carbon  deposits  appear  in  the  cylinders.  The  adjustment  of 
the  gas  mixture  is  therefore  of  importance,  the  normal  ratio  for  aviation  engines  being 
one  part  of  gasoline  to  9  to  20  parts  of  air. 


88 


Practical    Aviation 


(c)    Committee  on  Public  Information. 

Student  aviators  of  the  Signal  Corps,  U.  S.  A.,  learning  in  the  ground  school  how  valves 
are  adjusted  and  ignition  timed  on  aeronautic  motors 


Motor  Cautions  and  Trouble  Chart  89 

IMPORTANT  DON'TS 

Don't  forget  to  inspect  the  motor  thoroughly  before  starting. 

Don't  try  to  start  without  oil,  water,  or  gasoline;  all  three  are  vital. 

Don't  forget  to  see  that  the  radiator  is  full  of  water. 

Don't  get  dirt  or  water  into  the  oil. 

Don't  get  dirt  or  water  into  the  gasoline. 

Don't  forget  to  oil  all  exposed  working  parts. 

Don't  try  to  start  without  retarding  the  magneto ;  a  serious  accident  may 
result. 

Don't  try  to  start  without  turning  on  the  switch. 

Don't  start  the  motor  with  throttle  wide  open. 

Don't  run  the  motor  idle  too  long;  it  is  not  only  wasteful  but  harmful. 

Don't  forget  to  watch  the  lubrication ;  it  is  most  essential. 

Don't  forget  that  the  propeller  is  the  business  end  of  the  motor ;  treat  it 
with  profound  respect — especially  when  it  is  in  motion. 

Don't  cut  off  the  ignition  suddenly  when  the  motor  is  hot ;  allow  it  to  idle 
for  a  few  minutes  at  low  speed  before  turning  off  the  switch.  This  insures 
the  forced  circulation  of  the  water  till  the  cylinder  walls  have  cooled  con- 
siderably and  also  allows  the  valves  to  cool,  preventing  possible  warping. 

Don't  fail  to  study  the  trouble  chart  before  you  molest  a  thing  about  the 
motor,  if  you  have  trouble. 

Don't  develop  that  destructive  disease  known  as  tinkeritis;  when  the 
motor  is  working  all  right,  let  it  alone. 

Don't  forget  a  daily  inspection  of  all  bolts  and  nuts.  Keep  them  well 
tightened. 

Don't  fail  to  stop  your  motor  instantly  upon  detecting  a  knock,  a  grind, 
or  other  noise  foreign  to  perfect  operation.  It  may  mean  the  difference  be- 
tween saving  or  ruining  the  motor. 

THE  TROUBLE  CHART 

Based  on  Curtiss  engines,  this  chart  has  been  prepared  to  outline  in  a 
simple  manner  the  various  troubles  that  interfere  with  the  efficient  action  of 
aeronautical  motors. 

Defects  that  may  develop  are  tabulated  for  ready  reference,  and  opposite 
the  part  affected  the  various  conditions  are  found  under  a  heading  that  de- 
notes the  main  trouble  to  which  the  others  are  contributing  causes. 

The  various  symptoms  denoting  the  individual  troubles  outlined  are  given 
to  facilitate  their  recognition  in  a  positive  manner.  Brief  note  is  also  made  of 
the  remedies  for  the  restoration  of  the  defective  part  or  condition. 

It  is  apparent  that  a  chart  of  this  kind  is  intended  merely  as  a  guide,  and 
it  is  a  compilation  of  practically  all  the  known  troubles  that  may  materialize 
in  gas-engine  operation.  While  most  of  the  defects  outlined  are  common 
enough  to  warrant  suspicion,  all  will  never  exist  in  an  engine  at  the  same 
time;  and  it  will  be  necessary  to  make  a  systematic  search  for  such  of  those 
as  do  exist,  and  by  the  process  of  elimination  locate  the  offending  part. 

To  use  the  chart  advantageously  it  is  necessary  to  know  and  recognize 
easily  one  main  trouble.  For  example,  if  the  motor  is  skipping,  look  for 
possible  troubles  under  the  heading  "Skipping."  If  the  motor  fails  to  develop 
power,  the  trouble  will  undoubtedly  be  found  under  "Lost  Power  and  Over- 
heating." 

It  is  assumed  in  all  cases  that  the  trouble  exists  in  the  power  plant  or  its 
components,  and  not  in  the  auxiliary  members  of  the  ignition.  In  many  in- 
stances, however,  the  seat  of  trouble  will  be  traced  to  these  latter  members. 


90 


Practical    Aviation 


SKIPPING  OR  IRREGULAR  OPERATION 


PART  AT  FAULT 

TROUBLE 

EFFECT 

REMEDY 

Spark  plug 

Loose  binding  at  post 
Leak  in   threads 
Defective  gasket 
Cracked  insulator 
Points    too    close 
Points  too  far  apart 
Carbon  deposit 
Plug  too  long 

No   spark 
Low  compression 
Low  compression 
Short-circuit 
No  spark 
No  spark 
No  spark 
Pre-ignition 

Tighten   terminal 
Screw  down  tighter 
Replace  with  new  plug 
Replace  with  new  plug 
Set  points  apart 
Set  points  closer 
Clean  off  points  and  plug 
Change  plug 

Combustion   chamber 

Carbon  deposit 

Pre-ignition 

Remove  carbon 

Piston  head 

Carbon  deposit 
Crack  or  blowhole   (rare) 

Pre-ignition 
Pre-ignition 

Remove  carbon 
Replace  with  new 

Valve  head 

Warped  or  pitted  on  seat 

Poor   mixture 
Low  compression 

True  up  in  lathe  and  grind 
to  seat 
Replace  with  new 

Valve  stem 

Binds  in  guide  sticks 

Irregular   valve   action 

Clean  guide 
Straighten  stem 
Oil 

Valve  spring 

Weakened  or  broken 

Irregular  valve   action 

Replace  with  new 

Exhaust  valve   seat 

Scored  or  warped 
Dirty  or  covered  with 
scale 

Valve  will  not  close 
Poor  mixture 
Poor  compression 

Use  reseat  reamer 
Clean  off  and  grind  to  seat 

Exhaust  valve-stem  £uide 

Warped  or  carbonized 
Worn  guide 

Valve  stem  sticks 
Low  compression 
Poor  seating 
Poor   mixture 

Clean  guide  or  new  guide 

Valve-stem   clearance 

Too  little 
Too  much 

Valve  will  not  shut 
Valve  opens  late  and  closes 
early 

Set  inlet  gap  0.010 
Set  exh.  gap  0.010 

Camshaft  bearing 

Looseness  or  wear 

Valves    mistimed    or    valve 
lift   short 

Replace  with   new  bushing 

Cam 

Worn  contour 

Valve  lift  short 
Valves  mistimed 

Replace      with     new     cam- 
shaft 

Timing  gear 

Not  properly  meshed 
Loose  on  shaft 
Worn  or  broken  tooth 

Valves  mistimed 
Valves  do  not  act 

Time  properly 
Fasten  to  shaft  with  key 
Replace  with  new  gear 

Cam-follower  guide 

Loose  on  engine  base 
Lock  pin  sheared  off 
Worn  in  bore 

Oil  leaks 
Poor  valve  action 

Fasten   securely 
New  pin 
New  guide  or  bushing 

Cam  follower 

Loose  in  guide 

Valves  mistimed 
Oil   leaks 

Replace  with  new  guide  or 
bushing 

Inlet  valve 

Closes  late 
Opens  early 

Blowback  in  carburetor 

Time  properly 

Inlet-valve   seat 

Warped  or  pitted 
Does  not  seat  properly 
Carbon  grain  under  seat 

Blowback  in  carburetor 
Low  ci-mpression 

Use  reseat  reamer 
Clean  off  and  grind  to  seat 

Inlet-valve  stem  guide 

Worn 

Poor  mixture 
Low  compression 

Bush    or    replace   with    new 
guide 

Carburetor 

Weak  mixture 

Blowback  in  carburetor 

Adjust  carburetor  for  richer 
mixture 

Gas  manifold  pipe 

Leak  at  joints 
Defective    gasket 
Crack  or  blowhole 

Poor  mixture 
Poor  mixture 
Poor  mixture 

Stop  all  leaks 
Replace  with  new 
Solder  blowhole 

Piston 

Walls  scored 

Poor    suction    and    leak    of 
gas 

Smooth  up 

Piston   rings 

Loss  of  spring 
Loose  in  grooves 
Worn  or  broken 
Slots  in  line 

Poor    suction    and    leak    of 
gas 

Poor  compression 

Peen   rings  or  replace   with 
new 

Loosen  rings  on  piston 

Cylinder  wall 

Scored  by  wristpin 
Scored  by  lack  of  oil 

Poor    suction    and    leak    of 
gas 
Poor  compression 

Lap  in  cylinder 
Or  new  cylinder 

Valve-spring  collar  key 

Broken 

Release  spring 
No  valve  action 

Replace  with  new  key 

The    Trouble    Chart 


91 


LOST   POWER   AND    OVERHEATING 


PART  AT  FAULT 

TROUBLE 

EFFECT 

REMEDY 

Manifold  connections 

Poor  mixture  in  one  set  of 
cylinders  with  good  mix- 
ture in  other  set 

Surging  or  pulsating 

Tighten  connections;  put  in 
new  gaskets 

Water-pipe  .pint 

Loose 
Defective  gasket 

Loss    of    vater    and    over- 
heating 

Tighten     bolts     or     replace 
with  new  connection 

Spark  plug 

Loose  in   threads 
Defective  gasket 

Poor  compression  and  over- 
heating 

(See     Spark     Plug     under 
"Skipping") 
Screw  down  tight 
Replace  with  new 

Combustion    chamber 

Crack  or  blowhole 
Roughness 

Carbon  deposit 

Poor  compression 
Pre-ignition 

Pre-ignition 

Fill   by   welding  or   replace 
with  new 
Smooth  up 
Remove  carbon 

Valve  head 

Warped,   scored,   or  pitted 
Carbonized  or  covered  with 
scale 

Poor  compression 

True  up  in  lathe  and  grind 
to  seat 
Scrape     off     smooth     with 
emery  cloth 

Valve  seat 

Warped  or  pitted 
Carbonized  or  covered  with 
scale 

Poor  compression   or  blow- 
back 

Use  reseat  reamer 
Clean  off  and  grind  to  seat 

Piston  rings 

Loss  of  spring 
Loose  in  groove 
Worn  or  broken 
Slots  in  line 

Poor   suction,    leak   of   gas, 
and  over-heating 
Poor  compression 

Peen  rings  or  replace  with 
new 
Loosen  rings  on  piston 

Piston  rings 

Broken  because  too  tight 
Insufficient   opening 

Scored  cylinder  walls,  over- 
heating in  sump  pan,  and 
poor  compression 

Replace    scored    cylinder    if 
groove  is  deep;   use  new 
rings 

Wristpin 

Loose 
Scored  cylinder 

Poor  compression 

Fasten  securely 
Replace    scored   cylinder    if 
groove   is   deep 

Piston  head 

Carbon  deposit 
Crack  or  blowhole  (rare) 

Pre-ignition 
Poor  compression 

Remove  carbon 
Replace  with  new 

Piston 

Binds  in  cylinder 
Walls    scored   or   worn    out 
of  round 

Overheating 

Lap  off  excess  metal 
Replace  with  new 

Cylinder  wall 

Scored 
Poor   lubrication  causes 
friction 

Poor  compression  and  over- 
heating 

Replace  with  new 
Lap  in  cylinder 
Repair  oiling  system 

Camshaft 
Drive  gear 

Loose  on  shaft 
Not  properly  meshed 
Worn  or  broken  teeth 

Irregular  valve  action 

Fasten  to  shaft 
Time   properly 
Replace  with  new 

Crank  shaft 

Scored    or    rough    on    jour- 
nals 
Sprung 

Overheating 
Overheating 

Smooth  up 
Straighten 

Crankpin 
Bearings   and  main   bear- 
ings 

Adjusted  too  tight 
Defective  oiling 

Overheating 

Adjust  to  running  clearance 
Clean  out  oil  holes 

Oil   sump 

Insufficient  oiling 
Poor  oil 

Dirty  oil 

Overheating     and     burned- 
out  bearings 

Replenish   supply 
Use    best    oil  —  Mobile    "A" 
recommended 
Wash   with   kerosene 
Replace  with  new  oil 

Water    space    and    water 
pipes 

Clogged    with    sediment    or 
scale 

Overheating 

Dissolve    and    remove    for- 
eign material 

Radiator  hose 

Layer     of     hose      obstructs 
opening 

Overheating 

Refit  or  replace  with  new 

Water  pump 

Impeller  loose   on   shaft 
Dirty 
Broken 

Overheating 

Fasten  to  shaft 
Clean 
Replace  with  new 

92 


Practical    Aviation 


NOISY    OPERATION 


PART  AT  FAULT 

TROUBLE 

EFFECT 

REMEDY 

Spark  plug 

Leakage 

Hissing 

Screw  down  tighter 
Replace  with  new 

Cylinder  wall 

Scored 

Knocking 

Smooth  up  or  replace 
with   new 

Manifold   pipe   joints 

Leakage 
Defective  gaskets 

Sharp  hissing 

Tighten  bolts 
Replace  with  new 

Combustion   chamber 

Carbon   deposit 

Knocking 

Remove  carbon 

Cylinder  casting 

Retaining  bolts  loose 

Sharp  metallic  knock 

Tighten  bolts 

Cam 

Worn  contour 

Metallic  knock 

Replace  with  new 

Piston  head 

Carbon    deposit 

Knock 

Remove  carbon 

Wristpin 

Loose  in  piston 
Worn 

Dull  metallic  knock 

Replace  or  bush 

Connecting  rod 

Worn   at  wristpin   or  crank 
shaft 
Sideplay   in   piston 

Distinct  knock 

Adjust  or  replace 
Scrape  and  fit  and  oil 

Main  crank  shaft  bearing 

Loose 
Defective    lubrication 

Metallic  knock 
Squeak 

Fit  caps  close  to  shaft 
Clean  out  oil  holes  and  oil 

Connecting-rod  bearings 

Loose 
Excessive  play 
Binding 

Intermittent  metallic  knock 
Knock   and   squeak 

Refit 
Reline 

Connecting-rod    bolts 
Main-bearing  bolts 

Loose 
Stripped   threads 

Sharp   knock 

Tighten 
Replace   bolts 

Lower    half    crank    case 
bolts 

Loose 
Stripped   threads 

Knock  and  rattle 

Tighten 
New  bolts 

Water  jacket 

Covered  with  scale 
Clogged  with   dirt 

Knock  caused  by  overheat- 
ing 

Dissolve     scale     and     flush 
out      water      space      with 
water  under  pressure 

Timing  gears 

Loose 
Worn  or  broken  teeth 
Meshed   too    deeply 

Metallic  knock 
Rattle 
Grinding 

Fasten    to    shaft 
Replace  with  new  gear 

Camshaft  bearing 

Loose   or  worn 

Slight  knock 

Replace  with  new 

Inlet-valve  seat 

Warped  or  pitted 
Dirty 

Rattle 
Poor  compression 
Blowback 

Use  reseat  reamer 
Clean  off  and  grind  to  seat 

Inlet-valve  spring 

Weak  or  broken 

Blowback   in   carburetor 

Replace  with  new 

Inlet  valve 

Closes  late 
Opens  early 

Blowback   in   carburetor 

Time  properly 

Valve-stem  guide 

Worn  or  loose 

Rattle  or  click 

Replace  with  new  guide 

Cam-follower  guide 

Loose 

Rattle  or  click 

Replace  with  new  guide 

Valve-stem  clearance 

Too  much 
Too  little 

Click 
Blowback   in    carburetor 

Set  inlet  pap  0.010 
Set  exh.  gap  0.010 

Push-rod  retention 
stirrups 

Nuts  loose 

Rattle 
Blowback   in    carburetor 

Tighten  nuts 

Crank  case  gaskets 

Leak 

Oil  leak 

Tighten  bolts 
Replace  with  new 

Cylinder  or  piston 

No  oil 
Poor  oil 

Grinding  and  sharp  knock 

Repair  oil  system 
Use  best  oil 

Piston 

Binding  in  cylinder 
Worn     oval,     causing     side 
slap 

Grind   or   dull   squeak 
Dull  hammer 

Lap  off  excess  metal 
Replace  with  new 

Oil  sump 

Insufficient  oil 
Poor   oil 

Grind     and     squeak    in     all 
bearings 

Replenish  with  best  oil 

Piston   rings 

Defective  oiling 

Squeak,  hiss,  grind 

Replace  with  new  ring 
Repair  oil  system 

Crank  shaft 

Defective  oiling 

Squeak 

Clean   out  oil   holes 
Use  bes'.  oil 
Repair  oil  system 

Engine  base 

Loose   on   frame 

Dull  pound 

Tighten  bolts 

Practical    Aviation  93 


REVIEW  QUIZ 

Types  of  Motors,  Operation  and  Care  of  Engines 

1.  State  the  relation  to  efficiency   of  an  engine  with  a  short  stroke 

running  at  high  speed.    At  low  speed. 

2.  Name  four  advantages  gained  by  increasing  the  number  of  cylinders 

in  aviation  engines. 

3.  Why  is  the  V  construction  best  for  multi-cylindered  engines? 

4.  Explain  how  the  length  of  the  crank  shaft  of  an  8-cylinder  V-motor 

is  practically  the  same  as  that  of  a  4-cylinder  vertical  engine. 

5.  Describe  two  methods  of  attaching  connecting  rods  in  pairs  to  one 

crank  throw. 

6.  Give  the  number  of  power  impulses  per  revolution  of  a  12-cy Under 

motor. 

7.  State  and  weigh  the  respective  values  of  the  advantages  and  dis- 

advantages of  rotary  engines. 

8.  Briefly  describe  the  operations  of  the  Gnome  engine. 

9.  State  the  positions  and  duties  assigned  to  five  mechanicians  required 

when  an  airplane  prepares  for  flight. 

10.  Explain  how  the  propeller   should  be  grasped  for  cranking,  with 

particular  reference  to  first  and  second  positions  of  the  feet. 

11.  If  the  engine  fails  to  start  what  action  is  required  before  repeating 

the  operation? 

12.  Give  the  full   set  of  signals  which  governs  the  acts  of  pilot  and 

mechanician  during  preparation  for  immediate  flight. 

13.  How  does  a  compressed  air  self-starter  turn  the  motor  over? 

14.  By  an  example,  explain  how  fuel  may  be  conserved  for  long  flights. 

15.  In  what  way  does  altitude  affect  the  amount  of  power  secured  from 

the  engine? 

16.  Give  twelve  important  precautionary  acts  of  motor  inspection  before 

starting. 

17.  When  the  explosive  charge  in  cylinders  ignites  too  soon  what  parts 

should  be  examined?       Suggest  two  remedies  when  the  fault  is 
located. 

18.  Name  five  parts  which  should  be  examined  if  the  motor  is  over- 

heating. 

19.  When  a  knock  or  a  grind  is  detected  what  should  be  done  instantly? 

20.  Describe  the  character  of  the  noise  which  warns  of  a  defective  con- 

necting rod  bearing. 


94  Practical    Aviation 


CHAPTER  ANALYSIS 

Instruments  and  Equipment  for  Flight 

AVIATOR'S   EQUIPMENT: 

(a)  Clothing. 

(b)  Goggles. 

(c)  Watch. 

(d)  Safety  Belt. 

AIRPLANE  INSTRUMENTS: 

(a)  Scope  and  Usefulness. 

(b)  Cockpit  Arrangement. 

(c)  Gauges. 

(d)  Compass. 

(e)  Barometer  or  Altimeter. 

(f)  Tachometer. 

(g)  Angle  of  Incidence  Indicator, 
(h)  Inclinometer. 

(  i)  Radiator  Temperature  Indicator. 

(j)  Drift  Meter, 

(k)  Air  Speed  Meter. 

(1)  Banking  Indicator. 


CHAPTER  X 


Instruments  and  Equipment  for  Flight 


Before  beginning  consideration  of  actual  flight,  a  preliminary  survey  of  the 
aviator's  equipment  and  aids  is  advisable.  These  consist  of  his  clothing  and 
accessories  and  the  instruments  which  aid  navigation  of  the  air.  Many  argu- 
ments are  advanced  for  the  method  of  instruction  by  which  the  pilot  acquires 
a  sense  of  "feel"  without  dependence  upon  mechanical  devices,  but  while 
this  instinctive  knowledge  is  essential,  intelligent  use  of  the  instruments 
undoubtedly  increases  the  aviator's  efficiency. 

Clothing — A  warm  coat  is  a  necessity,  for  even  in  summer  it  is  cold  at 
high  altitudes.  In  winter  a  fur  lining  is  advisable;  in  ordinary  moderate 
weather  the  service  uniform  covered  by  a  leather  coat  is  sufficient.  Pockets 
without  flaps,  closing  by  an  elastic  band,  should  be  of  generous  size  so  that 
papers  may  be  easily  put  away  with  one  hand.  Warm  socks  are  essential 
and  soft  boots  or  puttees  without  straps  should  be  worn  with  the  riding 
breeches.  Fleece-lined  soft  leather  gauntlets,  allowing  easy  freedom  of  fingers 
and  wrists,  are  the  proper  protection  for  the  hands.  A  padded  helmet  is  a 
necessity.  The  aim  in  selecting  clothing  is  to  provide  flexibility  of  movement 
and  protection  from  the  cold  with  the  minimum  of  straps  and  strings  to 
catch  on  the  obstructions  within  the  cockpit.  Above  all,  clothing  must  be 
comfortable. 

Goggles — As  a  protection  from  the  wind,  even  though  the  airplane  be 
provided  with  a  wind  shield,  goggles  should  be  used  to  take  the  strain  off  the 
eyes.  Glass  lenses  should  not  be  used;  they  should  be  made  of  colorless 
celluloid  with  a  green  shade  at  the  top  and  bound  by  a  stiff  rubber  rim 
shaped  to  conform  to  the  face.  A  small  piece  of  chamois  should  be  carried 
to  wipe  off  the  flying  oil. 

Watch — An  accurate  timepiece  with  a  wrist  strap  is  essential  to  the 
military  aviator.  , 

Safety  Belt — Under  no  circumstances  should  the  aviator  venture  aloft 
without  his  safety  belt  adjusted.  This  device  consists  of  a  wide  web  of  heavy 
webbing  with  a  quick  detachable  locking  device.  The  belt  should  be  securely 
adjusted  with  the  stress  coming  at  the  thighs. 

95 


96 


Practical    Aviation 


Jj?c//nometer...... 

Oil  gauge'^    ' 
Map  holder....      \ 


Figure  71 — General  view  of  a  typical  airplane  cockpit 

AIRPLANE  INSTRUMENTS 

SCOPE   AND   USEFULNESS 

As  with  any  class  of  travel,  reaching  the  destination  by  air  flight  requires 
knowledge  of  position.  The  aviator  obviously  must  also  know  the  direction 
of  his  machine  toward  the  horizontal.  In  or  above  the  clouds,  out  of  sight 
of  earth,  knowledge  of  these  essentials  must  be  gained  through  instruments. 
The  devices  required  for  air  navigation  must  be  compact  and  rugged,  light, 
reliable  and  accurate. 

GAUGES 

An  oil  gauge  definitely  indicates  the  amount  of  oil  in  the  crank  case,  an 
oil-pressure  gauge  accurately  indicating  undisturbed  flow  and  the  pressure 
in  the  oil  system.  The  gasoline  gauge  registers  the  quantity  of  gasoline 
available  in  the  tanks,  preferably  by  mechanical  means. 

LUMINOUS   DIALS 

Paints  and  compounds  which  illuminate  pointers  and  figures  on  instru- 
ment dials  are  now  in  general  use,  electric  lighting  having  been  largely 
done  away  with  because  of  the  glare  and  the  vibration  to  which  lights  are 
subjected.  Zinc  sulphide  combined  with  radium  are  the  main  constituents  of 
the  most  reliable  luminous  paints. 

COCKPIT    ARRANGEMENT 

Wherever  practicable,  well  upholstered  seats  are  provided  for  aviators 
and  in  many  cases  comfort  is  further  promoted  by  passing  heated  exhaust 
pipes  through  the  cockpit.  Figure  71  shows  a  typical  arrangement  of  the 
pilot's  seat  and  dash  with  air  navigation  instruments  in  position  of  easy 
visibility. 


Compass,  Altimeter  and  Tachometer 


97 


Figure  72 — A  military  airplane  compass 


Figure  73 — The  barometer  or  altimeter 


COMPASS 

Air  navigation,  as  well  as  sea,  requires  the  aid  of  the  compass,  a  device 
which  contains  a  magnetic  needle  constantly  pointing  to  the  magnetic  north. 
In  the  aviation  compass  illustrated  in  Figure  72  a  compensating  attachment 
counteracts  stray  magnetic  influences.  The  card,  or  graduated  scale,  floats 
in  a  mixture  of  alcohol  contained  in  the  inner  bowl,  the  latter  being  bedded 
in  horsehair,  which  absorbs  vibration.  The  alcohol  varies  in  proportion  to 
water  from  45  per  cent  to  almost  pure  alcohol,  the  high  percentage  being 
maintained  to  prevent  freezing  at  high  altitudes. 

BAROMETER  OR  ALTIMETER 

To  indicate  the  height  of  the  airplane  above  the  earth  is  the  function 
of  the  instrument  illustrated  in  Figure  73.  Essentially,  it  comprises  a  vacuum 
chamber  which  is  acted  upon  by  the  varying  density  of  the  air.  The  dial  is 
adjusted  to  zero  on  the  ground.  Location  of  the  instrument  on  the  airplane 
is  of  great  importance  by  reason  of  the  possibility  of  influence  by  velocity 
pressure. 

TACHOMETER 

This  instrument,  not  illustrated,  is  in  all  essentials  similar  to  the  speed- 
ometer used  for  automobiles,  except  that  it  registers  the  number  of  revolu-  \ 
tions  of  the  motor.     Its  importance  may  be  estimated  by  considering  that  the 
power  delivered  by  the  engine  is  directly  related  to  its  speed  of  revolution 
and  that  the  speed  of  its  turning  may  be  used  to  compute  the  airplane's 
speed  relative  to  the  air.     Tachometers  are  either  magnetic  or  electric,  the  ! 
former  type  consisting  of  a  magnet  rotated  by  a  flexible  shaft  coupled  to  the  \ 
engine,  and  the  latter  comprising  a  generator,  engine  driven,  electrically  con- 
nected to  an  ammeter.    With  both  types  the  indications  are  made  by  a  needle 
and  graduated  arc  on  the  dash. 


98 


Practical   Aviation 


o 

I 


-s:  ^ 

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3    Cs    g 


1 


-       ^ 


Incidence  Indicator  and  Inclinometer 


99 


Figure  74 — Angle  of  incidence  indicator 


Figure  75 — An  inclinometer  Figure  76— -Engine  temperature  meter 

ANGLE  OF  INCIDENCE  INDICATOR 

This  device,  illustrated  in  Figure  74,  is  mounted  on  a  forward  strut  clear  of  the 
influence  of  the  propeller  and  the  body.  The  vane,  which  remains  level  when  the  air- 
plane is  in  motion,  has  a  pointer  and  indicator  graduated  in  degrees  and  visible  to  the 
aviator.  The  instrument  shows  the  angle  between  the  chord  of  the  wings  and  the  flight 
path.  By  means  of  a  dry  battery  and  electrical  connections  the  round  light  bank  shown 
is  attached.  When  the  flight  is  level  no  light  shows.  A  white  lamp  signals  when  a  dive 
is  made  at  too  steep  an  angle.  A  red  light  warns  of  an  angle  close  to  the  stalling  point. 
A  green  light  indicates  the  best  climbing  angle. 

INCLINOMETER 

Two  types  of  inclinometers  are  illustrated.  The  spirit-level  type  shown  mounted 
on  the  dash  in  Figure  71,  is  inaccurate  in  the  presence  of  accelerations  and  has  gen- 
erally been  superseded  by  the  instrument  illustrated  in  Figure  75.  This  device  registers 
the  angle  of  the  airplane  with  the  horizontal,  the  scale  being  on  a  weighted  wheel 
which  is  damped  by  floating  in  liquid,  which  insures  sensitiveness  and  increases 
accuracy.  The  scale  tips  forward  or  backward  with  the  angle  of  the  airplane,  the 
dial  being  mounted  on  the  instrument  board  in  the  cockpit. 

RADIATOR  TEMPERATURE  INDICATOR 

The  value  of  this  device,  illustrated  in  Figure  76,  is  obvious  when  it  is  considered 
that  great  altitudes  are  attained  by  airplanes  and  the  necessity  of  knowing  whether  the 
motor  is  getting  cold  Equally  important  is  knowledge  of  imminent  overheating.  The 
instrument  is,  therefore,  designed  to  register  from  freezing  to  boiling. 


100 


Practical    Aviation 


Figure  78 — Air  speed  meter 


Figure  77— The  drift  meter 


Figure  79 — Banking  indicator 
DRIFT  METER 

The  purpose  of  this  instrument,  shown  in  Figure  77,  is  to  enable  the  aviator  to 
remain  on  a  given  course  to  his  destination,  irrespective  of  drift  occasioned  by  side 
winds.  The  device  comprises  a  telescope  pointing  vertically  to  the  earth  with  hairs 
crossing  the  field  of  vision.  A  scale  and  pointer  indicates  the  angle  of  drift  in  degrees 
and  the  compass  lubber  line  moves  automatically  to  correct  for  any  existing  drift.  The 
instrument  is  widely  used  for  cross-country  flight. 

AIR  SPEED  METER 

This  mechanism  shows  the  airplane's  rate  of  speed  relative  to  the  air.  It  serves  to 
correct  for  the  aviator  any  erroneous  impressions  which  may  be  gained  by  his  speed 
in  relation  to  the  ground,  since  that  speed  varies  according  to  whether  his  airplane  is 
flying  with  or  into  the  wind.  It  is  also  useful  to  indicate  excessive  gliding  speed, 
straightening  out  from  which  may  stress  the  machine  to  dangerous  limits.  The  prin- 
ciple of  its  operation  is  pressure  of  wind  on  a  liquid  contained  in  a  tube,  a  lead  from 
one  end  of  which  is  open  to  the  wind.  This  device  is  also  known  by  the  names, 
manometer  and  Pitot  tube. 

BANKING  INDICATOR 

The  proper  lateral  attitude  of  flight  is  shown  on  this  instrument  by  the  airplane 
outline  on  a  fixed  dial,  below  which  is  a  bar  rotating  from  the  center  and  controlled  by 
a  pendulum  inside  the  case.  When  the  indicator  bar  and  the  wing  outline  are  parallel, 
as  in  the  illustration,  Figure  79,  the  machine  has  the  proper  amount  of  bank.  The  pen- 
dulum swings  outward  in  proportion  to  the  radius  and  speed  of  the  turn,  and  when  the 
pilot  has  not  properly  banked  his  airplane  the  indicator  bar  will  be  out  of  parallel  with 
the  wing  outline  on  the  dial.  The  pilot  then  merely  operates  hi?  "-»-trols  in  the  indicated 
direction  until  the  parallel  is  again  registered.  The  instrument  is  of  special  value  to 
the  aviator  at  night  or  in  a  cloud  or  fog  when  human  sensibilities  are  not  dependable. 


Practical    Aviation  101 


REVIEW   QUIZ 

Instruments  and  Equipment  for  Flight 

1.  What  type  of  goggles  are  best  and  why  should  a  piece  of  chamois  be 

carried? 

2.  Is  there  any  occasion  when  an  aviator  should  make  a  flight  without 

first  adjusting  his  safety  belt? 

3.  What  is  the  function  of  the  compass? 

4.  Why  should  the  altimeter  be  located  in  a  position  where  the  airplane's 

velocity  will  not  affect  it? 

5.  What  are  the  two  types  of  tachometers? 

6.  How  many  electric  light  signals  are  given  by  the  angle  of  incidence 

indicator? 

7.  When  the  flight  is  level  no  light  shows;  which  lamp,  then,  indicates 

best  climbing  angle? 

8.  If  a  white  lamp  is  flashed  by  the  action  of  the  indicator,  what  does  it 

indicate  ? 

9.  Give  the  essential  difference  between  two  types  of  inclinometers  and 

state  what  these  instruments  register. 

10.  How  does  the  drift  meter  indicate  and  correct  the  angle  of  flight  in  a 

side  wind? 

11.  Explain  how  the  air  speed  meter  corrects  possible  erroneous  impres- 

sions of  the  velocity  of  the  airplane's  flight. 

12.  How  is  this  indicator  valuable  in  showing  gliding  speed? 

13.  Give  two  other  names  by  which  the  air  speed  meter  is  known. 

14.  What  is  the  relative  position  of  indicator  bar  and  wing  outline  on  the 

banking  indicator  when  the  airplane  is  properly  banked? 

15.  Under  what  flight  conditions  is  this  instrument  specially  valuable? 


102 


Aviation 


CHAPTER  ANALYSIS 

Instruction  in  Flying 
First  Flights  and  Gross-Gountry  Flights 


INSTRUCTION  IN  FLYING: 

(a)  The  Flying  Course. 

(b)  Junior  Military  Aviator  Tests. 

(c)  Flying  by  Dual  Control. 

(d)  Flight     Instruction     by     Solo 

Method. 

(e)  Military  Aviator  Course. 

(f)  Advanced  Flying. 

FIRST  FLIGHTS: 

(a)  Position  for  the  Start. 

(b)  Leaving  the  Ground. 

(c)  Climbing. 

(d)  Turning. 

(e)  Straightening  Out. 
-    (f)  S-Turns. 

(g)  Right  of  Way. 

(h)  Meeting  an  Airplane. 

(i)  Overtaking  an  Airplane. 

(j)  Meeting  at  an  Angle. 

(k)  Landing  Sites. 

(1)  Landing. 

(m)  Bad  Landings. 

CROSS-COUNTRY  FLIGHT: 

(a)  Equipment. 

(b)  Physical  Fitness. 

USE  OF  THE  COMPASS: 

(a)  The  Compass  Card. 

(b)  Compass  Error. 

(c)  Variation. 

(d)  Deviation. 

(e)  Adjusting  the  Compass. 

(f)  Placing  the  Compass. 

LAYING  OFF  A  COURSE: 

(a)     Determining      the      Steering 
Direction. 


(b)  Data  Required. 

(c)  Preparing     a     Diagram     for 

Wind  Factor. 

(d)  Radius  of  Action. 

SOME  FLIGHT  CONSIDERA- 
TIONS: 

(a)  Proper  Preparation. 

(b)  Height. 

(c)  Air  Disturbances. 

(d)  Lost  Bearings. 

(e)  Landmarks. 

(f)  Time  Checking. 

(g)  Selecting  Landings, 
(h)     Forced  Landings, 
(i)     Pegging  Down. 

(j)     Re-Starting. 

MAP  READING: 

(a)  Definition  of  Terms. 

(b)  Orienting. 

(c)  The  Scale. 

(d)  Contours. 

(e)  Conventional  Signs. 

(f)  Map  Preparation. 

THE  FLYING  CREW: 

(a)  The  Navigator. 

(b)  The  Pilot. 

(c)  The  Observer. 

(d)  Motor  Engineer. 

(e)  The  Gunner. 

(f)  Radio  Operator. 

THE  REPAIR  CREW: 

(a)  Aviation  Mechanician. 

(b)  Assistant  Chief  of  Crew. 

(c)  Mechanician  Helpers. 


CHAPTER    XI 

Instruction  in  Flying 
First  Flights  and  Gross-Gountry  Flights 

The  theory  of  aviation  may  now  be  said  to  be  fully  covered  and  the  stu- 
dent ready  for  text  on  actual  flight.  If  the  preceding  chapters  have  been  care- 
fully studied  there  is  no  flight  evolution  of  the  airplane  which  is  not  entirely 
understandable  to  the  reader.  The  function  and  operation  of  the  airplane  as  a 
whole,  and  its  controlling  means  as  separate  and  unified  parts,  will  be  clear 
without  further  explanation  in  the  description  of  the  various  flight  maneuvers. 
One  point  may  well  be  repeated  here,  however,  to  fix  the  matter  clearly  in  the 
student's  mind.  That  is  the  results  of  operation  of  the  stick  control  and  rud- 
der, which  may  be  simplified  as  follows : 

To  go  down,  push  the  stick  control  forward. 

To  rise,  pull  it  back. 

To  tilt  to  the  left,  push  it  left. 

To  tilt  to  the  right,  push  it  right. 

To  turn  left,  rudder  with  left  foot. 

To  turn  right,  rudder  with  right  foot. 

Thus  it  is  seen  that  the  movements  are  the  natural  ones;  for  example,  if 
the  airplane  is  tilted  sideways  to  the  right  the  natural  tendency  is  to  lean  left. 
Pulling  the  stick  to  the  left  rights  the  plane ;  and  so  on,  each  motion  being  the 
automatic  one,  so  to  speak. 

During  early  stages  of  flight  training  the  pupil  must  not  hesitate  to 
tell  the  instructor  if  at  any  time  he  feels  physically  or  temperamentally  unfit. 
Flying  when  not  mentally  inclined  for  the  instruction  will  quickly  ruin  an 
aviator's  prospects  for  later  success,  and  any  hesitancy  about  stating  his  con- 
dition for  fear  of  a  "cold  feet"  accusation  is  not  to  be  tolerated.  Aviation  in- 
structors and  students  are  sympathetic,  earnest  men;  they  have  no  time  for 
taunts. 

Acquiring  confidence  in  early  stages  is  a  tremendous  help ;  until  it  is 
acquired  the  first  solo  flight  should  not  be  attempted ;  usually,  after  five  hours 
dual-control  instruction,  the  elementary  machine  may  be  flown  solo.  Some 
fifteen  or  twenty  flight  hours  on  various  elementary  types  is  generally  suf- 
ficient, and  the  faster  airplanes  may  then  be  used.  Take-offs  and  landings 
should  be  frequent  in  practice,  for  nothing  more  quickly  instills  confidence 
than  knowledge  that  the  matter  of  alighting  has  been  mastered. 

In  this  chapter,  the  scope  of  the  preliminary  training  will  be  considered 
by  progressive  steps,  a  survey  of  the  whole  subject  being  given  by  first  defining 
the  composition  and  duties  of  the  flying  and  repair  crews  and  the  tests  for 
grading  as  an  aviator, 

103 


104  Practical    Aviation 


INSTRUCTION  IN   FLYING 

Candidates  for  instruction  in  aviation  in  the  U.  S.  Army  are  selected  from 
the  following  sources: 

Officers  of  the  line  of  the  Army. 

Enlisted  men  of  the  Aviation  Section,  Signal  Corps. 

Civilian  aviators,  employed  as  Instructors. 

Civilian  aviators,  employed  to  perform  flying  duties  and  given  the  rank 

of  Aviator,  U.  S.  Army. 
Officers  and  enlisted  men  of  the  Signal  Officers  and  Signal  Enlisted 

Reserve  Corps. 


THE  FLYING  COURSE 

The  instruction  is  divided  into  definite  stages  comprising  a  complete  flying 
course,  as  follows : 

(a)  Preparatory. 

(b)  Preliminary. 

(c)  Elementary. 

(d)  Advanced. 

The  preparatory  instruction  includes  all  the  teaching  up  to  the  point 
where  the  pupil  actually  takes  hold  of  the  controls  while  the  craft  is  in  flight 
through  the  air.  Preliminary  training  may  be  defined  as  the  instruction  up 
to  the  point  where  the  student  makes  a  flight  alone,  making  quarter,  half  or 
full  turns.  Elementary  training  is  the  stage  of  instruction  preliminary  to  the 
completion  of  pilot's  tests.  Advanced  flying  is  the  next  step  up  to  the  qualifi- 
cation tests  as  a  junior  military  aviator. 


JUNIOR    MILITARY    AVIATOR   TESTS 

(a)  Five  figures-8  around  pylons,  keeping  all  parts  of  the  machine  inside 
of  a  circle  with  a  radius  of  300  feet. 

(b)  Climb  out  of  a  field  1,200x900  feet  and  attain  500  feet  altitude,  keep- 
ing all  parts  of  the  machine  inside  of  the  field  during  climb. 

(c)  Climb  3,000  feet,  kill  motor,  spiral  down,  changing  direction  of  spiral, 
that  is  from  left  to  right,  and  land  within  150  feet  of  a  previously  designated 
mark. 

(d)  Land  with  dead  motor  in  a  field  800x100  feet,  assuming  the  field  to 
be  surrounded  by  a  10-foot  obstacle. 

(e)  From  500  feet  altitude,  land  within  100  feet  of  a  previously  desig- 
nated point,  with  a  dead  motor. 

(f)  Cross-country  triangular   flight  of  approximately   60  miles  without 
landing. 

(g)  Straightaway    cross-country    flight,    without    landing,    of    about   90 
miles. 


Flight  Instruction  Methods  105 


FLYING    BY    DUAL    CONTROL 


THE  AIRPLANE 


A  machine  of  moderate  power  and  slow  speed  is  used,  with  large  surfaces 
for  slow  landing  speed.  Dual  controls  are  provided,  so  that  either  instructor 
or  student  can  control  the  craft. 

FIRST  STAGE 

The  student  merely  observes  the  operations  of  the  instructor  at  the  be- 
ginning. He  is  given  the  "feel"  of  the  air  and  taught  to  gauge,  by  the  air 
pressure  against  face  and  body,  his  speed  and  flotation  for  horizontal  flight, 
climbing  and  banking.  The  machine's  response  to  the  controls  is  noted  and 
their  resistance  to  motion  observed. 

SECOND  STAGE 

Instruction  is  given  in  the  operation  and  management  of  the  controls. 
Horizontal  flights  are  followed  by  broad,  flat  turns,  quarter,  half  and  full 
circles  to  right  and  left,  simple,  normal  landings  and  take-offs  and  balancing 
the  airplane  in  the  air.  Flight  through  unfavorable,  disturbed  air  is  next 
performed,  including  banking,  climbing  and  gliding,  moderate  spiral  glides 
and  straight  and  spiral  volplanes.  Landings  of  various  kinds  are  then  taught, 
including  normal,  slow-speed*  pancake  and  stall  landings,  and  landing  in  wind. 
The  instructor  gradually  turns  over  the  air  controls  to  the  student  as  the  in- 
struction progresses,  and  finally  the  power  controls.  Taxying,  or  maneuvering 
the  machine  on  the  ground,  is  also  mastered  before  the  student  takes  to  the 
air  alone. 

FLYING  ALONE 

Detailed  instructions  as  to  the  flight  course  and  maneuvers  to  be  per- 
formed are  given  by  the  instructor  before  the  student  flies  alone,  and  the 
altitude  is  also  prescribed.  The  first  flight  alone  is  elementary,  being 
restricted  to  horizontal  flight,  take-offs  and  landings  on  a  straight  course. 
It  is  followed  by  adding  circles  to  right  and  left,  moderate  climbs  and  straight 
glides.  Figures  eight  are  made  with  gradually  decreasing  radii  and  steeper 
banking;  the  turns  are  then  combined  with  glides  and  advanced  to  spiral 
glides.  From  both  straight  and  spiral  glides,  landings  are  then  made  with 
a  dead  motor.  The  instructor  watches  his  pupil  closely  from  an  observation 
tower  during  these  flights  and  corrects  all  faults  observed  at  the  completion 
of  the  flight. 


106  Practical    Aviation 


FLIGHT    INSTRUCTION    BY    SOLO    METHOD 

FIRST  STAGE 

The  first  machine  used  for  this  method,  practically  one  of  self-training  by 
progressive  use  of  selected  airplanes,  is  low  powered  with  small  lifting  sur- 
faces, in  fact  not  intended  for  use  off  the  ground.  The  speed  of  propeller 
revolution  is  limited  by  a  stop  on  the  engine  throttle.  The  student  first  learns 
the  manipulation  of  controls  from  the  pilot's  seat,  that  is,  the  rudder,  elevators 
and  balancing  planes,  or  ailerons.  He  is  then  taught  to  "taxi"  on  the  ground, 
using  a  straightaway  course  on  a  broad,  flat  and  hard  path,  and  to  acquire 
skill  in  steering  the  machine  on  the  ground. 

SECOND  STAGE 

The  next  machine  is  one  of  limited  power  but  designed  to  lift  off  the 
ground  for  a  height  of  about  two  feet,  the  lift  being  regulated  by  the  throttle 
of  the  engine.  The  limitation  of  power  causes  the  machine  to  sink  gently 
back  on  the  ground  but  permits  the  student  to  master  the  operation  of  the 
elevator.  Hops  up  to  200  feet  are  made  in  this  way  and  the  handling  of 
balancing  planes  is  accurately  learned.  From  then  on  the  machine  is  regulated 
gradually  until  straightaway  flight  is  made  at  heights  up  to  20  feet,  several 
take-offs  and  landings  being  required  with  each  flight. 

THIRD  STAGE 

The  next  machine  is  of  an  advanced  type  and  in  it  flights  are  made  at  an 
altitude  of  50  feet,  at  which  very  slight  curves  are  taken  along  the  course. 
Increasing  altitudes  are  attained  and  these  curves  are  gradually  advanced  to 
circles,  with  greater  angle  of  banking  for  decreased  radius  or  increased  speed ; 
these  are  mastered  by  barely  perceptible  degrees.  Broad  figures  of  eight 
follow  and  straight  and  spiral  glides  under  throttled  power  advance  to  glides 
without  power,  or  the  volplane.  Accuracy  in  landing  on  a  mark  and  coming 
to  rest  over  a  mark  are  then  attained. 

COMBINATION  OF  TRAINING  METHODS 

Where  time  permits,  the  best  training  course  is  a  combination  of  solo  and 
dual  methods,  the  former  to  give  the  student  self-reliance  and  the  dual  con- 
trol instruction  to  correct  any  errors  acquired  in  training. 

MILITARY   AVIATOR  COURSE 

Advanced  flying  is  begun  with  training  designed  to  perfect  judgment  in 
landings  and  the  volplane.  Difficult  conditions  are  then  imposed,  the  flyer 
being  taught  to  handle  his  machine  near  buildings,  fences  and  all  classes  of 
obstructions,  first  on  the  ground  and  then  in  the  air.  He  is  trained  to  rise  and 
land  over  imaginary  obstacles  or  over  a  specified  height,  indicated  by  a  string 
stretched  between  two  posts  and  marked  by  a  pennant.  He  ascends  from  and 
descends  into  fields  of  restricted  area,  which  for  safety  are  marked  by  chalk 
lines. 

High-powered  machines  and  unfavorable  weather  are  selected  and  sharp  turns, 
steep  banks,  spiral  glides  and  difficult  landings  are  practiced.  The  instruction  is  mainly 
designed  to  give  the  pilot  confidence  in  his  abilities  and  to  impress  upon  him  caution 
and  thoroughness. 

The  elementary  observer's  course  consists  of  progressive  flights  at  increasing 
altitudes  and  under  varying  conditions  of  visibility,  from  clear  weather  to  foul.  Visi- 
bility tests  with  naked  eye  and  field  glasses  of  various  powers  are  made,  followed  by 
instruction  flights  in  reconnaissance  and  navigation  of  the  air.  Short  cross-country 
flights  in  preparation  for  junior  military  aviator  tests  are  then  in  order. 

These  tests  complete  the  training  as  a  military  pilot;  further  development  is 
acquired  by  training  on  various  types  up  to  super-planes  and  high  speed  pursuit  planes. 
Expert  aviators  are  required  to  attain  a  minimum  altitude  of  12,000  feet,  remain  in 
flight  for  four  hours  and  cover  200  miles,  cross-country. 


Instruction  in  Flying 


107 


ADVANCED    FLYING 

The  advanced  work  is  classified  by  the  Training-  Department  of  the  Army 
Aviation  Schools  into  special  phases  as  follows : 

Excessive  use  of  controls 

Reduced  power  flights 

Flat  glides 

Steep  climb 

Banking  up  to  90° 

Fast  landings  and  take-offs 

Landing  across  wind 

Stalls,  side-slips,  tail-slides,  loops 

Bad  weather ;  rain 

Water  flying 

Night  flying 

Altitude  flights ;  duration  flights ;  cross-country  flights 

Passenger  carrying  and  low  flying 

The  course  of  study  and  practical  work  embraces  the  elements  of  aeronau- 
tical engineering,  use  of  meteorological  and  aeronautic  instruments ;  advanced 
meteorology;  practical  reconnaissance;  spotting  artillery  fire;  bomb  drop- 
ping; principles  of  aerial  combat;  wireless  telegraphy;  gunnery;  strategic 
and  tactical  employment  and  administrative  control  of  the  air  squadron. 


Photo  Com.  Pub.  Inf. 

American  beginners  in  France  receiving  solo  instruction  on  the  elementary  non-flying  machine 


108 


Practical    Aviation 


mam 


Duties  of  Airplane  Crews  109 


THE   FLYING   CREW 

An  airplane's  flying  crew  is  largely  governed  by  the  type  of  machine. 
Small  machines  of  high  power,  designed  either  for  strategic  reconnaissance 
flights  or  pursuit  at  high  speeds,  carry  but  a  single  aviator.  The  two-seater, 
or  most  common  airplane  carries  an  observer  or  gunner.  Aircraft  of  the 
super-plane  class  carry  from  3  to  15  men,  comprising  additional  duties  of 
navigator,  gunner,  engineer  and  radio  operator. 

THE  NAVIGATOR 

Military  control  and  direction  of  pilot,  gunners,  bombers,  radio  operator 
and  engineers,  as  well  as  the  navigation  of  the  machine  in  flight,  is  the  duty  of 
the  navigator,  usually  the  senior  officer  of  the  crew. 

THE  PILOT 

Management  of  the  controls  of  the  airplane  while  in  flight  is  the  duty  of 
the  pilot.  He  is  also  responsible  for  final  inspection  of  the  craft  before  the 
flight  is  begun,  and  for  the  careful  completion  of  any  repairs  or  alterations  on 
the  machine.  Immediately  upon  return  from  a  flight  it  is  his  duty  to  examine 
minutely  all  controls,  lifting  surfaces  and  braces  and  supervise  all  mechanical 
adjustments  not  included  in  shop  work. 

THE  OBSERVER 

Preparation  of  reconnaissance  maps  and  reports,  all  observations  and 
computations  of  flight  navigation,  is  the  duty  of  the  observer.  In  combat  he 
directs  the  fire  against  enemy  airplanes  and,  if  on  a  bombing  expedition, 
orders  the  use  of  explosive  or  incendiary  bombs  according  to  the  objective. 
He  is  also  responsible  for  the  efficiency  of  the  personnel  of  the  crew  and  the 
materiel. 

MOTOR  ENGINEER 

Uninterrupted  operation  of  the  motor  or  motors  in  flight  is  the  responsi- 
bility fixed  on  the  motor  engineer.  At  all  times  he  performs,  with  the  help 
of  an  assistant,  any  work  necessary  to  insure  the  highest  operating  efficiency 
of  the  airplane's  engines,  and  is  responsible  for  all  repairs  other  than  those 
required  to  be  made  in  the  machine  shop. 

THE  GUNNER 

Expertness  in  the  care  and  operation  of  machine  guns  and  the  construc- 
tion and  operation  of  explosive  and  incendiary  bombs  is  required  of  the  gun- 
ner. Range-finding,  loading  and  releasing  devices  for  bombs  and  telescope 
and  air  compressor  must  also  be  thoroughly  mastered. 

RADIO  OPERATOR 

Installation  of  apparatus,  assembly  and  dismantling  of  radio  equipment, 
thorough  knowledge  of  all  codes  of  army  signaling,  are  qualifications  of  the 
radio  operator.  In  addition,  he  is  responsible  for  all  communications  from 
the  airplane  and  must  be  familiar  with  the  operation  of  visual  signaling 
devices,  such  as  the  Very  pistol,  rockets,  smoke  bombs,  etc. 


110  Practical   Aviation 


THE    REPAIR    CREW 

Two  non-commissioned  officers  and  three  privates,  first  class,  are  gen- 
erally assigned  to  an  airplane  and  are  responsible  for  its  care  on  the  ground. 
In  the  case  of  small  airplanes  the  repair  crew  may  consist  of  only  three  men, 
but  the  general  practice  is  a  crew  of  five. 

AVIATION  MECHANICIAN 

The  chief  of  the  repair  crew  is  rated  first  class  sergeant  or  sergeant,  and 
in  the  U.  S.  Army  is  known  as  Aviation  Mechanician.  He  is  responsible  for 
the  condition  of  the  airplane  and  its  materiel  while  it  is  in  the  hangar;  he 
supervises  all  adjustments,  alterations,  installations  and  repairs.  All  property 
issued  for  maintenance  and  all  tools  and  accessories  are  in  his  charge,  and 
he  is  responsible  for  the  cleaning  and  preservation  of  the  craft. 

ASSISTANT  CHIEF  OF  CREW 

Rated  as  a  sergeant  or  a  corporal,  the  assistant  aids  the  chief  and  is 
required  to  be  a  qualified  mechanic  capable  of  discharging  all  duties  of  the 
chief  of  crew. 

MECHANICIAN  HELPERS 

The  three  mechanician  helpers,  rated  as  privates,  first  class,  are  under  the 
orders  of  the  chief  of  crew  and  his  assistant.  They  are  required  to  assist  in 
adjustments,  alterations,  removals,  installations  and  repairs,  to  clean  the 
motor  and  all  parts  of  the  airplane  fuselage  and  surfaces,  fittings  and  fixtures, 
wires  and  cables.  It  is  their  duty  to  keep  the  hangars  clean  at  all  times ;  to 
replace  tools  and  equipment ;  to  elevate  the  machine  on  chocks  or  jacks  when 
in  its  stall  and  to  cover  the  motor  propellers  and  cockpit.  Hauling  gasoline, 
oil  and  other  supplies  and  assisting  in  repair  work  are  among  their  duties. 
When  not  employed  about  the  machine  they  are  required  to  be  available  for 
instruction  or  duty  in  the  machine  and  repair  shop. 


First  Flights 


Figure  80 — An  airplane  headed  into  the  "wind,  the  position  for  the  start 


Figure  81 — Taxying  at  the  start  with  wheels  on  the  ground  and  tail  raised 

FIRST  FLIGHTS— THE  START 

The  airplane  should  be  turned  directly  against  the  wind,  as  this  position 
aids  the  initial  rise  from  the  ground  and  makes  it  easier  to  maintain  balance, 
a  difficult  matter  in  a  cross  wind. 
LEAVING  THE  GROUND 

The  engine  should  be  developing  full  power  for  the  required  thrust  before 
the  signal  is  given  for  the  mechanicians  to  let  go.  As  the  airplane  starts 
forward  along  the  ground,  the  tail  stabilizer  is  depressed  by  moving  its  control 
forward.  This  causes  the  tail  to  rise  from  the  ground  and  places  the  lifting 
surface  more  horizontal,  offering  less  resistance  as  rolling  speed  is  acquired. 
Figure  81  illustrates  this  position.  When  the  machine  is  taxying  at  a  velocity 
equal  or  greater  than  the  airplane's  low  flying  speed,  the  tail  control  is 
pulled  back  gently  and  held.  The  tail  end  of  the  machine  then  drops  and  the 
angle  of  incidence  of  the  wings  is  increased,  causing  the  airplane  to  rise. 

A  minimum  distance  of  100  yards  (covered  in  5  to  10  seconds,  according  to  the 
wind)  is  allowed  between  the  starting  point  and  the  rise  from  the  ground. 

CLIMBING 

The  tail  control  is  pulled  back  slightly  and  held  fixed  in  the  new  position, 
further  increasing  the  lifting  surface  angle  of  incidence.  The  motor  is  then 
accelerated  to  its  proper  climbing  speed. 

The  airplane  should  be  pointed  into  the  wind  for  the  first  200  feet  of  altitude  and 
the  student  flier  should  rise  at  least  100  feet.  A  landing  made  from  a  lesser  height  is 
valueless  for  instruction  purposes. 


112 


Practical   Aviation 


Djrect/on  of/c/rn 

\         /-^  -Kucfder  fur/)e<y 


J/'/eron  up 


4//eron  down 


d/Jeron  tfo>vn 


4 Heron 


r/ 

$$}  0/recf/b/i  of 
stfe  s//p 


Figure  82 — A   turn  made  too  flat  Figure  83 — Too   steep   banking 

TURNING 

Turning  with  the  novice  almost  invariably  reveals  one  fault,  i.  e.,  the 
banking  is  too  steep.  This  must  be  corrected  before  the  aviator  attempts  the 
steep  turns.  The  following  general  rules  will  prove  useful  in  learning  to  turn 
the  airplane  correctly. 

A  good  altitude  margin  should  be  allowed,  so  there  will  be  at  least  500  feet  to 
correct  for  bumps  or  side-slips. 

First  turns  should  be  very  wide  and  not  through  more  than  180  degrees,  or 
half-turn. 

While  turning,  speed  should  be  kept  up  to  at  least  level  flying  speed,  and  the 
airplane  nosed  down  to  its  normal  gliding  angle.  If  flying  speed  is  lost,  the  machine 
will  side-slip  or  stall,  getting  into  the  cabre,  or  tail  down,  position  which  is  dangerous 
to  the  novice. 

As  the  natural  tendency  is  to  lose  height,  it  is  best  to  turn  the  airplane  against 
the  wind  at  first. 

Aileron  and  rudder  controls  should  be  handled  gently  and  first  turns  made 
gradual  ones. 

Figures  82  and  83  show  turns  improperly  made.  A  turn  top  flat  causes  an  out- 
ward side-slip,  and  too  steep  banking  an  inward  side-slip.  Either  of  these  faults 
are  perceptible  to  the  aviator  by  the  feel  of  the  wind  on  his  face.  During  a  right 
turn,  for  instance,  a  noticeable  wind  on  the  opposite,  or  left,  cheek  indicates  an  out- 
ward side-slip.  This  is  corrected  by  gently  pushing  the  stick  to  the  right  for  more 
bank  or  turning  the  foot  bar  for  less  rudder.  When  the  opposite  effect  on  the  cheek 
is  noticed,  more  rudder  and  less  bank  is  required. 

Gradually,  turns  may  be  made  smaller  until  a  2^-turn  spiral  in  1,000  feet  is 
accomplished.  Turning  while  volplaning  may  then  be  tried. 

In  gliding  turns  the  airplane's  nose  should  be  kept  below  the  line  of  the  horizon. 
Climbing  turns  require  the  nose  of  the  machine  above  the  horizon. 

STRAIGHTENING  OUT 

A  few  simple  rules  will  serve  to  teach  how  to  come  out  of  a  turn  properly. 

Theoretically,  the  rudder  and  aileron  controls  are  brought  back  to  central  posi- 
tions. In  many  airplanes,  however,  they  must  be  brought  over  to  the  opposite 
bank  first  and  centered  when  the  machine  is  level.  The  stick  control  should  be 
moved  a  trifle  sooner  than  the  rudder,  and  brought  past  center,  being  returned  to 
central  position  when  the  rudder  is  at  center  and  the  airplane  at  a  horizontal  level. 

Coming  out  of  a  steep  turn  these  control  movements  are  made  greater,  the  stick 
being  given  a  semi-circular  action.  Special  care  should  be  taken  that  the  rudder  is 
not  swung  over  opposite  too  early,  for  this  will  throw  the  nose  of  the  airplane  up 
and  an  inward  side-slip  will  result. 

S-TURNS 

These  are  a  series  of  descending  Figure  8s  or  S-turns,  useful  for  landing  in  a 
restricted  area.  Two  rules  should  be  followed.  During  the  entire  turn  the  aviator 
should  keep  his  eye  on  the  landing  spot  selected  and  always  turn  toward  that  point. 
The  turns  are  made  increasingly  smaller  as  the  ground  is  approached  for  the  final 
glide. 

Turning  near  the  ground  should  be  avoided;  speed  should  be  maintained  by 
keeping  the  nose  down. 


Rules  of  the  Air 


113 


About 


100  yds 


Figure  84 — The  overtaking  airplane  steers  Figure   85    (Upper} — Distance   for  passing  in 
clear   about    100   yards   of   the   slower  opposite  directions 

machine     ahead    and     avoids     the  Figure  86    (Lower) — How  an   airplane  gives 
disturbed  air  of  the  backwash  way  to  one  met  on  its  right 

RIGHT  OF  WAY  IN  THE  AIR 

The  student  aviator  should  acquaint  himself  with  the  air  rules  of  the 
flying  school  to  which  he  is  assigned.  The  courses  are  usually  prescribed  and 
the  direction  of  circuits  and  pylon  markings  clearly  stated.  While  slight 
variations  may  be  encountered  at  various  flying  fields,  the  following  general 
rules  are  almost  universally  observed : 

OVERTAKING  AN   AIRPLANE 

The  faster  machine  coming  from  the  rear  maintains  the  minimum  distance,  100 
yards,  by  steering  clear,  care  being  taken  that  the  overtaking  machine  is  not  brought 
within  the  zone  of  influence  of  the  backwash,  for  in  the  disturbed  air  rough  going 
will  be  encountered.  See  Figure  84. 

MEETING   AN    AIRPLANE 

When  an  airplane  is  encountered  coming  in  the  opposite  direction,  both  machines 
keep  to  the  right  and  pass  at  a  minimum  distance  of  100  yards.  See  Figure  85. 

MEETING  AT  AN  ANGLE 

In  a  situation  such  as  illustrated  in  Figure  86,  where  two  airplanes  approach  at 
an  angle,  the  aviator  who  finds  the  other  machine  on  his  right  gives  way. 

LANDING  SITES 

The  United  States  Army  requires  of  a  flying  field  for  testing  aviators  a  minimum  size  of  800  by  100 
feet.  The  general  area  of  a  field  is  about  9  acres,  200  yards  square.  Area  allowances  are  added  for 
obstacles,  proportionately  based  on  the  obstacle's  height,  12  times  the  height  being  added  to  the  area,  or 
12  feet  of  field  depth  added  for  every  foot  of  obstacle  height. 

The  above  regulation  applies  only  to  machines  of  slow  landing  speed.  When  fast  airplanes  are 
used,  the  200-yard  depth  is  added  to  as  follows:  40  m.p.h.,  60  yards;  45  m.p.h.,  120  yards;  50  m.p.h., 
360  yards;  55-60  m.p.h.,  960  yards.  These  dimensions  are  based  on  landing  and  taking  off  against  the  wind. 

Plowed  fields,  soft  ground  and  ditches  are  dangerous  to  the  inexperienced  aviator  and  should  be. 
avoided  as  landing  places. 

Canvas  strips,  15  feet  long  and  3  feet  wide,  are  usually  employed  to  identify 
landing  sites.  These  are  visible  to  the  pilot  at  altitudes  up  to  9,000  feet  and  indicate 
to  the  airman  the  direction  for  approach.  The  strips  are  arranged  in  the  form  of 
a  T,  the  approximate  outline  of  the  airplane;  a  long  strip  is  laid  crosswise  below  the 
T  to  mark  the  point  of  contact  with  the  ground,  the  machine  being  brought  to  full 
stop  when  on  the  T  itself. 


114 


Practical    Aviation 


L/ne  of  f//ghf 


Line  of  f//gftf 


Figure  88 — The  pancake  landing 


Figure  87 — Airplane  gliding 


LANDING 

Making  a  proper  landing  is  one  of  the  most  difficult  and  most  important 
tasks  that  confront  the  student  aviator.  The  success  of  the  landing  is  largely 
dependent  upon  nosing  the  machine  down  at  the  proper  distance  from  the 
landing  field  and  choosing  the  proper  gliding  angle.  Thus,  if  the  angle  is  1  in 
6%  and  the  machine  is  at  200  foot  elevation  the  maximum  distance  allowed 
for  the  descent  would  be  200  X  6^  =  1300  feet  from  the  landing  spot  selected. 
If  a  greater  distance  is  allowed,  the  machine  is  liable  to  fall  short.  A  distance 
less  than  this  maximum  is  preferred,  since  a  spiral  may  be  made  to  kill  extra 
height  and  a  correction  of  gliding  angle  made  if  the  angle  selected  is  not  the 
best.  All  airplanes  are  designed  to  assume  their  gliding  angle  with  power  and 
thrust  cut  off. 

OPERATION  OF  CONTROLS 

When  the  descent  is  to  be  made  the  engine  is  throttled  down  to  relieve  strains 
on  the  airplane  and  insure  flexibility  of  controls.  Since  the  proper  gliding  angle  is 
determined  by  the  speed,  the  tachometer  or  the  air  speed  indicator  should  register 
the  determined  speed  within  5  miles  an  hour.  The  machine  should  be  headed  directly 
into  the  wind,  the  direction  of  which  may  be  determined  by  observation  of  chimney 
smoke  or  flags  below.  When  within  15  feet  of  the  ground  the  tail  control  is  gently 
pulled  back,  elevating  the  tail  until  the  airplane  is  in  its  horizontal  position  for  slow 
flight.  This  should  be  accomplished  when  5  feet  above  the  ground  and  the  control 
then  held;  the  airplane  will  thereafter  descend  without  further  assistance.  The  control 
should  be  held  lightly,  however,  to  correct  for  bumps. 

"When  about  to  effect  a  landing  a  glance  should  be  directed  to  the  horizon  or  the 
banking  indicator,  and  the  aileron  control  used  to  keep  the  airplane  laterally  level. 
Swerving  as  the  machine  touches  the  ground  is  corrected  by  the  rudder  or  the  tail  skid. 

BAD  LANDINGS 

If,  when  the  airplane  is  about  to  land,  it  assumes  the  position  of  flight 
shown  in  Figure  88  it  will  bounce  when  it  strikes  the  ground,  the  running 
gear  breaking  on  the  second  impact.  Also,  if  brought  out  of  gliding  position 
when  too  high  off  the  ground  it  will  drop,  due  to  lack  of  speed,  and  the  same 
break  follow.  These  landings  are  known  as  the  "pancake."  The  remedy  is 
to  speed  up  the  motor  to  regain  velocity  and  flying  position,  then  throttle 
down  and  land. 

The  most  dangerous  landing  is  caused  by  failure  to  pull  the  airplane  from 
gliding  to  flying  position,  the  running  gear  striking  the  ground  at  a  forward 
inclined  angle.  The  motor  must  be  instantly  opened  wide  after  the  first 
bounce,  flying  speed  being  regained  before  the  rebound. 

A  bad  landing  which  severely  strains  landing  gear  and  causes  wheels  to  buckle, 
follows  contact  with  the  ground  when  the  rudder  is  turned,  causing  a  swerve,  or 
when  the  airplane  is  not  level  laterally. 


Equipment  for  Long  Flights 


115 


PREPARATIONS    FOR   CROSS-COUNTRY    FLIGHT 

Qualifying  tests  for  Junior  Military  Aviator  prescribe  two  cross-country 
flights,  one  of  approximately  60  miles  and  the  other  90  miles.  When  these 
flights  are  undertaken  the  student  aviator  is  expected  to  know  all  the  funda- 
mental technique  of  flying,  turning  and  landing,  and  have  reached  the  stage 
where  the  operation  of  controls  is  no  longer  a  task  but  a  matter  of  instruction 
routine,  so  to  speak;  in  flying  cross-country,  therefore,  he  is  enabled  to  give 
a  large  share  of  attention  to  following  the  course  and  selecting  proper  places 
should  an  emergency  landing  be  required.  Prior  to  the  flight  a  few  matters  of 
importance  require  attention. 

EQUIPMENT 

The  usual  flying  clothing  is  worn,  the  only  caution  being  to  provide  for  sufficient 
warmth.  Leather  suit  and  helmet  are  worn,  supplemented  in  winter  by  sweaters  and 
mufflers.  Hands  anO  feet  are  most  sensitive  to  cold  and  should  be  well  protected; 
provision  of  large  boots  with  woolen  socks  or  stockings  will  repay  the  aviator  in 
comfort.  On  a  long  flight  it  is  well  to  take  two  pair  of  goggles,  in  case  one  pair 
should  be  lost  or  broken,  and  a  handkerchief  to  clean  them  is  necessary.  An  identifi- 
cation card  and  money  should  be  carried  for  emergencies;  the  telephone  number 
of  the  airdrome  should  also  be  noted  and  a  complete  set  of  tools  and  covers  for 
propeller  and  cockpit  should  be  carried. 


STANDARD    EQUIPMENT— AIRPLANE    TOOL    CHEST 


1   Saw,   hand,   26" 

1  Hammer,    riveting,    8   oz. 


1  Wrench,    Stillson,    14". 

1   Screwdriver,    8". 

1   Screwdriver,   7". 

1   Screwdriver,   5". 

1   Nail-puller. 

1   Knife,    draw   8". 


1  Bit,    expansive,    ^    to   3' 

1  Pliers,   round  nose,  6". 

1  Pliers,   snipe  nose,  4". 

1  Pliers,  adjustable,   8". 

1  Pliers,   side-cutting,  8". 

1  Pliers,  adjustable,  6". 


1   Stone,  carborundum,   5". 
1  Torch,   gasoline,  flat. 
1   Set.    thin     open-end     wrenches 
with    canvas   roll. 


(Cover) 

1   Combination   square,   bevel  and 
level,   12". 

(Top) 

1  Hammer,   tinsmith's,    1    pound. 
1  Hammer,    claw. 
1  Tape,    steel,    100   feet. 
1  Brace,    10". 

1  Iron,  soldering,  \y2  Ibs.,  1  iron, 

soldering,   jeweler's. 

(Upper   Drawer) 

2  Pliers,  auto,  combination  cutting, 

6  and  8". 

1  Nipper-cut,    7". 

2  Pliers,  diagonal,  6". 

1   Pliers,    compound,    side-cutting, 
8". 

(Lower   Drawer) 
1   Set  drills,  Morse,  straight  shank,     1  Wrench,    7". 

with  canvas  roll.  3   Reamers,    taper,    bit    stock, 


1   Rule,    folding. 
1  Hacksaw  frame. 
1    Dividers,    pair   6". 


2  Center    punches. 
24  Blades,      Hacksaw,      coarse;      12 
blades,   Hacksaw,  fine;    1  chisel, 
cold,    Y±";   1   chisel,  cold,    y2" '. 

1  Calipers,    6". 

1  Wrench,   monkey,   6". 


1  File   holder. 
1  Spoke   shave,    3". 
1  File  cleaner. 

10  Files,   assorted,   with  canvas  roll. 
1   Screwdriver,    4". 
1  Palm,  sewing;  8  needles,  assorted; 
1  ball  flax  and  1  ball  wax. 


1  Plane,    block,    15-6". 
1   Drill,    hand. 


5-16,  and 
1  Hatchet,  half  (small). 
1   Snips,   tinner's. 


The  machine  should  be  carefully  inspected,  from  tires  to  instrument  board,  before 
the  start.  Wires,  controls,  engine  and  gasoline  and  oil  reservoirs  are  matters  to  be 
looked  into  by  the  aviator,  who  must  not  accept  the  word  of  mechanicians  that  every- 
thing is  ready.  The  instruments  required  are  a  compass,  wrist  watch,  altimeter, 
tachometer,  inclinometer  and  a  map  board  or  case.  The  map  case  is  highly  preferable 
as  maps  pinned  to  a  board  often  blow  off  or  are  torn  in  long  fast  flights. 

The  map  is  a  most  important  part  of  the  aviator's  equipment  for  a  cross-country 
flight.  It  should  be  placed  in  a  position  of  easy  visibility,  such  as  on  the  instrument 
board,  or,  in  any  event,  as  nearly  as  practicable  straight  ahead  in  the  line  of  vision. 
The  course  should  be  carefully  mapped  out  and  notations  made,  as  discussed  in  suc- 
ceeding pages.  On  a  long  journey  a  weather  report  obtained  by  telephone  from  the 
point  of  destination  may  save  trouble  should  fogs  or  storms  be  prevalent  there. 

PHYSICAL  FITNESS 

The  aviator  should  have  no  hesitation  in  informing  his  instructor  or  flight  com- 
mander of  any  indisposition;  if  he  does  not  feel  well  a  cross  country  flight  should 
not  be  attempted,  as  the  correct  functioning  of  all  his  faculties  will  be  required.  A 
long  flight  on  an  empty  stomach  is  bad,  as  dizziness  often  results.  At  least  a  hot 
drink  should  be  secured,  and  a  good  meal  if  possible.  Food  in  tablet  form,  chocolate 
or  biscuits  may  be  taken  along,  but  should  be  placed  in  a  position  of  easy  access. 


116 


Practical    Aviation 


Compass  Variation  and  Deviation  117 


Figure  89 — Compass  card     Figure  90 — Vertical  Figure  91 — Adjusting  the  compass 

Compass 

USE    OF    THE    COMPASS    AND    ITS    ADJUSTMENT 

The  compass  is  an  instrument  for  indicating  the  magnetic  north  by  a 
magnetized  needle  on  a  pivoted  card.  While  cross-country  flight  is  possible 
with  the  aid  of  a  map  and  identifying  landmarks,  at  times  when  these  are 
obscured  the  compass  is  a  necessity  to  the  aviator.  Steering  by  compass  ac- 
curately, reference  to  the  map  is  not  required  in  flight,  providing  preliminary 
calculations  are  accurately  made  as  later  outlined  in  this  chapter. 
THE  COMPASS  CARD 

The  card  is  illustrated  in  Figure  89.  Marking  in  degrees  is  clockwise,  the  circle 
beginning  at  N  (north)  as  zero,  and  comprising  360  degrees.  The  card  is  also 
marked  in  the  old  form  of  the  merchant  marine;  north,  east,  south  and  west  being 
represented  by  90  degrees,  bearings  being  read,  for  example,  20°  W.  of  N.  An 
aviation  compass  of  the  vertical  type  is  illustrated  in  Figure  90. 
COMPASS  ERROR 

VARIATION — The  compass  indicates  the  magnetic  north  from  any  given  place; 
i.  e.,  the  compass  magnet  points  to  the  north  magnetic  pole,  situated  on  a  northern 
Canadian  island.  This  is  not  the  "true"  north,  and  it  is  therefore  necessary  on  maps 
of  the  various  parts  of  the  earth  to  make  the  correction  known  as  variation.  This 
is  the  angle  between  the  true  and  magnetic  meridian  at  the  point  mapped. 

DEVIATION — Since  the  compass  needle  is  magnetic  and  the  airplane  contains 
much  metal  of  magnetic  attraction  an  error  known  as  deviation  is  caused  which  deflects 
the  needle  some  degrees  to  the  east  or  west. 

Adjusting  the  Compass — To  correct  the  deviation  error  is  a  task  seldom  assigned 
to  the  aviator,  but  some  idea  of  how  it  is  accomplished  will  be  found  of  value.  (The 
process  which  we  term  adjusting,  is  known  in  England  as  ''swinging"  the  compass.) 
The  airplane  is  placed  with  its  fore  and  aft  axis  exactly  north  and  south,  either  by 
aligning  it  with  a  tripod  "land"  compass  placed  nearby,  or  by  placing  the  airplane 
on  a  cement  slab  provided  for  the  purpose  in  many  flying  fields.  The  airplane  is 
trued  up,  in  the  latter  case,  by  spirit  level  and  plumb  line,  as  illustrated  in  Figure  91. 
The  compass  has  what  is  known  as  the  "lubber's  line,"  which  is  then  fitted  to  the 
fore  and  aft  line  of  the  airplane.  The  compass  reading  is  then  taken,  and  by  inserting 
small  field  magnets  in  slots  provided  for  the  purpose,  the  east  or  west  deviation  of 
the  needle  is  corrected  until,  it  points  north  with  the  cement  slab.  When  the  best 
correction  possible  has  been  made  a  deviation  card  is  generally  made  out  and  placed 
near  the  compass,  for  in  long  flights  to  a  definite  objective  an  error  as  small  as  2  or  3 
degrees  will  throw  out  the  aviator's  calculations.  A  specimen  of  these  cards  follows: 

For  Magnetic  Course  Steer  by  Compass  For  Magnetic  Course  Steer  by  Compass 

N  0  degrees  357  degrees  S.  180  degrees  183  degrees 

N  E  45        "  47        "  S.  W.  225        "  223 

E'  90        "  90        "  W.  270        "  270 

S.  E.  135        "  137        "  N.  W.  315        "  317 

PLACING  THE  COMPASS 

The  proper  location  of  this  instrument  is  an  important  matter.  It  should  be 
placed  in  clear  view  and  directly  in  front  of  the  pilot,  preferably  in  the  center  fore 
and  aft  axis  of  the  airplane,  as  far  as  possible  from  moving  metal  parts  such  as  those 
of  the  engine.  Metal  parts  such  as  control  levers  and  rods,  if  within  2  feet  of  the  com- 
pass, should  be  non-magnetic,  and  movable  equipment  such  as  machine  guns,  should 
be  in  normal  flying  position  when  the  compass  is  adjusted.  After  any  required  change 
in  parts  is  made  the  compass  deviation  should  be  checked  and  any  necessary 
readjustment  made. 


118 


Practical    Aviation 


Figure  92 — A  typical  military  map 


Soil  and  Cultivation. 


Enclosures 

Wire  fence 
Sarbe'd       *" 
Smooth 

N/XXN/X/X/ 


Communications 


Fill 

Cut 
Bridges. 


-      T  T  T  T 

/-•-  T.leg-aph. 


R.R.  double  track. 


River  Crossings. 


Figure  93 — Conventional  signs  for 
maps 


L 


Figure   94 — Height,   distance   and 
direction  symbols 


Meaning  of  Map  Signs  and  Symbols  119 

MAP   READING 

(Abstracted  from  Signal  Corps  Manual,  by  the  same  Author.) 

The  aviator  must  know  how  to  read  a  map  before  cross-country  flights 
can  be  made.  An  understanding  of  the  meaning  of  conventional  symbols  and 
application  of  the  scale  are  the  main  essentials,  extensive  knowledge  not  being 
necessary. 

A  typical  military  map  is  shown  in  Figure  92. 

DEFINITIONS  OF  TERMS 

In  mapping,  many  terms  are  used,  a  number  of  which,  such  as  basin,  crest,  gorge, 
knoll,  plateau,  and  watershed  are  universally  familiar.  A  few  special  terms  are  denned 
here,  however,  for  the  simplification  of  the  subject. 

Bearing — The  relative  position  or  direction  with  the  north,  or  true  meridian;  magnetic  bearing, 
the  relative  position  or  direction  with  the  magnetic  north. 

Contour — A  line  designating  the  shape,  outline  or  boundary  at  a  fixed  height  of  a  section  of 
ground;  contours  are  used  to  indicate  elevations,  each  contour  representing  a  rise  or  fall  in  feet  from 
those  surrounding  it.  Illustrated  by  A,  Figure  94. 

Gradient — This  indicates  a  slope  expressed  as  a  fraction,  a  gradient  of  1-50  designating  a  rise  of 
1  foot  in  50. 

Datum — A  fixed  level    (generally   sea   level)    from   which  all   heights  are   measured. 

Hachures — A  shading  method  of  representing  hills,  short  strokes  being  drawn  directly  down  the 
slopes.  Illustrated  by  B,  Figure  94. 

Meridian — A    true   north    and   south   line. 

ORIENTING 

The  first  thing  to  be  determined  is:  Where  is  the  north?  On  a  map  this  is  usually 
indicated  by  an  arrow  placed  in  one  of  the  corners.  Some  maps  do  not  have  an  arrow, 
in  which  case  it  is  a  generally  safe  assumption  that  the  top  of  the  map  is  the  north. 
When  two  arrows  appear,  as  in  D,  Figure  94,  one  points  the  true  north,  the  other  the 
magnetic  north.  Usually  they  are  so  marked,  but  if  not  lettered,  the  incomplete  or 
less  elaborate  arrow  represents  the  magnetic  north.  The  magnetic  north  is  the  north 
of  the  compass;  its  deviation  from  the  true  north  has  already  been  explained.  When 
the  map  has  been  turned  to  its  proper  position,  i.e.,  the  magnetic  north  arrow  cor- 
responding with  the  compass,  it  is  said  to  be  oriented.  This  is  the  first  step  for  the 
aviator  about  to  lay  out  a  cross-country  flight. 
THE  SCALE 

Having  located  his  position  on  the  map,  the  next  feature  for  the  aviator  to  study 
are  the  distances  between  points.  These  are  shown  by  the  scale,  which  appears  usually 
on  the  lower  end  of  the  map;  for  example,  two  points  are  measured  by  ruler  on  the 
map  and  the  distance  is  1  inch;  the  scale  reads:  1"  =  1  mi.  (as  in  C,  Figure  94),  then 
ihe  actual  distance  between  these  points  over  the  ground  will  be  found  to  be  1  mile. 
Some  maps  state:  (so  many)  miles  to  the  inch;  the  measuring  procedure  is  the  same, 
allowance  being  made  for  2  miles  to  the  inch,  or  whatever  the  scale  states.  What  is 
known  as  a  representative  fraction  is  sometimes  used.  On  the  map,  Figure'  92,  this 

appears  as  2112(7  '  ^  ^e  -^-^-  is  i™  it  means  that  an  inch  on  the  map  is  equal  to  100 
inches  on  the  ground;  the  fractions  are  usually  large,  such  as  >^  ^K  ,  which  would  indi- 
cate an  inch  to  a  mile,  since  there  are  63,360  inches  to  a  mile.  On  foreign  maps  im  000 

is  a  familiar  fraction,  and  may  indicate  either  inches  or  millimetres;  in  all  forms  the 
principle  is  the  same  and  the  scale  is  reckoned  in  the  same  way,  afterwards  being 
calculated  in  inches  by  the  aviator.  Another  method  of  showing  the  scale  is  illustrated 
on  the  map,  Figure  92,  where  it  is  only  necessary  to  copy  the  scale  on  a  strip  of  paper 
and  apply  it  directly  to  the  map,  reading  off  the  distances  between  any  designated  points. 
CONTOURS 

Contours  on  a  map  show  the  elevations,  depressions,  slope  and  shape  of  the  ground. 
Hachures,  (see  B,  Figure  94),  sometimes  used  on  European  maps,  show  elevations 
only  and  are  of  little  value.  The  method  of  indicating  features  by  contour  lines^  is 
clearly  shown  in  the  illustration  A,  Figure  94.  The  irregular,  curving  lines  which 
appear  on  the  map  represent  the  outlines  of  the  hill  at  equally  spaced  vertical  intervals. 
If,  for  example,  by  use  of  a  surveying  instrument  a  line  of  stakes  was  placed  around  a 
hill,  each  one  exactly  the  same  height  above  sea  level,  a  line  drawn  on  the  map  through 
all  the  stake  positions  would  be  a  contour.  Study  of  the  diagram  A,  Figure  94,  will 
make  it  clear  how  the  steepness  of  hillsides  is  determined  from  the  map,  contour  lines 
close  together  indicating  a  steep  slope,  and  far  apart,  a  gentler  slope. 

On  some  maps  contours  are  numbered  in  elevation  in  feet  above  the  datum  plane,  generally  sea 
level.  Thus,  at  a  glance,  the  elevations  are  clearly  determined. 

The  principal  conventional  signs  used  by  the  U.  S.  Army  are  given  in  Figure  93, 
and  should  be  memorized. 


120 


Practical    Aviation 


bo 


5 

g 

fcjO 

.e 
5 

10 

o\ 


Calculating     Drift 


121 


LAYING    OFF   A    COURSE 

DETERMINING  THE  STEERING  DIRECTION 

It  is  obviously  important  for  the  aviator  to  know  the  direction  to  head  his 
machine  to  arrive  at  a  given  destination.  When  flying  above  clouds,  over  water,  or 
at  night,  when  landmarks  are  not  discernible,  he  has  no  means  of  determining  how  far 
the  wind  may  be  blowing  him  off  his  course.  Calculations  are  therefore  made  in 
advance  by  the  following  method: 

DATA  REQUIRED: 

Flying  speed  of  his  airplane. 

Compass  bearing  of  his  course  from  point  of  departure  to  destination. 

Direction  and  speed  of  the  wind. 

The  map  of  the  country  over  which  he  is  to  fly  will  give  him  the  compass  bear- 
ings; the  points  joined  by  a  line  (see  Figure  94)  determine  the  direction  and  its  angle 
to  the  north  of  the  compass  bearing. 

Direction  and  speed  of  the  wind  can  be  found  from  the  weather  vane  and  anemo- 
meter of  the  airdrome.  The  anemometer  is  a  device  with  four  arms  carrying  cups  on 
the  end  of  each,  turning  about  on  a  vertical  axis  at  a  speed  varying  with  the  wind 
velocity.  When  the  wind  velocity  at  the  ground  has  been  determined,  the  aviator  must 
decide  upon  the  height  at  which  the  flight  is  to  be  made,  for  as  height  increases  the 
velocity  and  direction  of  the  wind  changes.  The  table  below  will  be  found  useful  in 
estimating  the  proper  allowance: 

WIND  VELOCITY  AND   DIRECTION   CHANGES  WITH   ALTITUDE 
(Based    on    Wind    Velocity    of    25    miles    per    hour) 


Height  in  feet  

At  the  earth's  surface 

500' 

1000' 

2000' 

3000' 

4000' 

5000' 

Velocity  change  in  per  cent.... 

100% 

135% 

172% 

188% 

196% 

200% 

200% 

Clockwise  deviation  in  degrees.. 

0 

5° 

10° 

16° 

19° 

20° 

21° 

Example:  Assume  that  the  anemometer  shows  a  wind  velocity  of  25  miles  per  hour  at  the  ground, 
and  the  weather  vane  indicates  the  direction  of  the  wind  89°  west  of  north.  The  aviator  plans  to  fly  his 
course  at  a  height  of  3000  feet.  From  the  table  he  learns  that  the  wind  velocity  at  this  altitude  is  196%, 
greater  than  at  the  ground;  then,  25X1.96  =  48  miles  per  hour.  Likewise,  from  the  table,  it  is  seen 
that  the  wind  direction  at  this  altitude  shows  a  clockwise  deviation  of  19°,  so  at  3000  feet  the  direction 
of  the  wind  will  be  89°  — 19°  =  70°  west  of  north. 


A  DIAGRAM  TO  DETERMINE  THE  WIND  FACTOR 

With  the  data  in  hand  the  aviator  can  lay  out  a  simple  diagram  for  his  course. 
Assume  that  his  orders  call  for  a  flight  from  Fort  de  Villeneuve  to  Bougy  (see  A-B, 
Figure  94).  The  route,  according  to  the  map,  is  30°  east  of  north.  The  speed  of  the 
aviator's  airplane  is  80  miles  per  hour.  The  wind,  as  already  determined,  has  a  velocity 
of  48  m.p.h.  in  a  direction  of  70°  west  of  north  at  3000  feet,  at  which  height  the  flight 
is  to  be  made. 

Either  on  the  map  or  on  a  separate  sheet  of  paper,  the  starting  point  is  designated 
A  (see  Figure  95).  A  line  is  then  drawn  with  the  proper  compass  bearing  to  the 
destination  B.  From  point  A  a  line  is  drawn  parallel  to  the  direction  of  the  wind,  blow- 
ing 70  degrees  west  of  north.  On  this  line  the  velocity  of  the  wind  is  measured  off,  the 
aviator  establishing  a  scale,  say  1  inch  =  10  miles,  or  any  other  convenient  scale.  Assume 
that  the  scale  1  inch  =  10  miles  is  the  one  selected;  then  48  m.p.h.  would  be  measured, 
4.8  inches  to  point  C.  With  a  pair  of  dividers  opened  to  represent  the  speed  of  the 
airplane  by  the  same  scale  (in  this  case,  80  m.p.h.  =  8.0  inches)  an  arc  is  described  with 
C  as  the  center.  Where  it  cuts  the  line  A-B  (see  D,  Figure  95)  a  line  is  drawn  from 
D  to  C ;  this  line  gives  the  proper  direction  to  steer  the  airplane  to  neutralize  the  drift 
of  the  airplane  in  one  hour's  flight  from  A  to  B  in  the  cross  wind.  The  steering  is  by 
compass  bearing  to  the  fore  and  aft  axis  of  the  machine. 

Measurement  of  the  line  A-D,  applied  to  the  scale  will  give  the  actual  velocity  in  miles 
per  hour  of  tire  flight.  In  the  example  it  is  seen  to  be  85  m.p.h.,  that  is,  the  cross  wind 
increases  the  airplane's  speed  5  miles  per  hour. 

The  student  should  reconstruct  the  diagram  for  the  return  flight.  That  it  will  not 
do  to  steer  in  exactly  the  opposite  direction  will  then  be  made  clear.  In  all  cross- 
country flights  a  separate  diagram  for  the  return  is  required,  unless,  of  course,  the  wind 
happens  to  be  exactly  parallel  to  the  course. 


122  Practical    Aviation 


RADIUS  OF  ACTION 

To  determine  the  distance  outward  the  airplane  can  go  and  have  sufficient  gasoline 
to  return,  requires  a  simple  calculation. 

The  aviator  knows  his  gasoline  capacity;  i.e.,  how  many  hours  of  flight  can  be 
obtained  before  the  tank  is  empty.  With  this  and  the  other  data  he  can  figure  his 
radius  of  action  in  miles. 

Example:  Assume  that  the  flight  is  to  be  made  straight  into  a  head  wind  of  30  miles  per  hour, 
the  speed  of  his  airplane  is  80  m.p.h.,  and  its  gasoline  capacity  4l/2  flight  hours.  (For  climbing  and  as 
a  general  margin  l/2  hour  gasoline  consumption  is  deducted,  leaving  4  flight  hours). 

On  the  outward  trip  his  speed  is  80  —  30  =  50    m.p.h. 

On  the  return  trip  his  speed  is  80  +  30=110  m.p.h. 

The  ratio  for  both  trips  is,  then,  as  50  is  to  110,  or  5  is  to  11.  The  time  required  for  the  outward 
trip  is  thus  11/16  of  4  hours,  and  the  return  trip  the  remaining  5/16  of  4  hours;  or,  outward  =  2^  hrs.; 
return  —1%  hrs.  Since  his  outward  bound  speed  is  50  m.p.h.,  then  50X2^  =  137^  miles  radius.  Return 


speed  being   110   m.p.h.,  then    110  X  1/4  —  137  i/t    miles.      This,   then,   is   the   radius   of   action. 

A  wind  blowing  directly  along  the  course  is  a  rare  occurrence,  however.  A  diagram 
similar  to  Figure  95  must  therefore  usually  be  made,  both  for  the  outward  and  return 
trips.  The  calculation  for  radius  of  action  is  then  carried  on  as  above,  or  by  the 
simple  formula: 

b  X  c  Where 

Radius  of  Action  =  a  X  -  I  Z  gas°lin5  hourj- 

b   I   c  b  =  outward  speed. 

c  =  return  speed. 

SOME   FLIGHT   CONSIDERATIONS 
PROPER    PREPARATION 

Care  must  be  observed  by  the  aviator  that  his  preliminary  preparations 
are  properly  made.  This  refers  particularly  to  a  study  of  the  course  from  the 
map. 

Ordinarily  the  country  over  which  he  is  to  make  the  flight  will  be  on  one 
sheet  with  features  and  landmarks  clearly  indicated.  Should  the  use  of  two 
sheets  be  necessary  these  should  be  pasted  together  before  starting  and  cut  to 
fit  the  map  roll.  In  war  flights  foreign  maps  with  the  scale  in  fractions  are 
often  the  only  ones  available;  the  aviator  should  immediately  construct  the 
corresponding  scale  at  so  many  miles  to  the  inch,  which  will  facilitate  rapid 
calculation.  Distances  from  the  starting  point  should  also  be  marked  at  ten 
mile  intervals  or  by  distinctive  objects  to  be  passed.  High  hills  should  be 
marked  as  bad  for  landing. 

HEIGHT 

Where  there  are  no  high  hills  or  mountains  in  friendly  territory  the  flight  is  best 
made  at  heights  from  1,500  to  3,000  feet.  An  altitude  of  1,500  feet  should  be  attained 
by  an  initial  circling  climb  before  the  aviator  sets  off  on  his  course.  Speed  and  steadi- 
ness of  wind  increases  with  height,  and  landing  or  righting  in  case  of  mishap  is  better 
accomplished  with  a  good  margin;  but  above  2,000  feet  contour  of  the  country  is  not 
readily  distinguished,  so  if  the  flight  is  to  be  at  a  higher  altitude  the  poor  landing 
places  should  be  clearly  marked  on  the  map.  It  is  well  for  beginners  to  keep  the 
ground  in  view  throughout  the  flight,  flying  under  or  around  any  clouds. 

CLOUDS,  FOG  AND  STORMS 

Pupils  are  cautioned  to  avoid  heavy  cloud  banks  and  not  to  rise  above  clouds 
when  near  the  seacoast,  for  a  wind  off  shore  may  carry  the  airplane  out  to  sea  with- 
out the  pilot's  knowledge.  When  navigation  above  a  cloud  bank  is  necessary,  the 
cloud  formations  may  be  used  as  a  basis  for  keeping  the  airplane  horizontally  level, 
for  cloud  formations  are  ordinarily  sufficiently  level  for  this  purpose.  Fog  should  be 
avoided;  in  fact,  when  a  heavy  mist  is  encountered  a  landing  should  be  made  as  soon 
as  possible.  River  valleys  should  be  avoided,  for  they  very  often  hold  a  ground  fog  up 
to  a  height  of  700  feet.  At  times  when  the  flight  must  be  continued  through  clouds 
or  fog,  the  instruments  should  be  carefully  watched  and  the  stick  control  and  rudder 
kept  in  central  position  as  much  as  possible.  Heavy  rain,  sleet  and  hail  chip  the  pro- 
peller slightly  and  when  encountered  a  landing  should  be  made  at  the  earliest  favorable 
opportunity.  A  whistling  sound  indicates  that  the  propeller  has  been  chipped. 


Remarks  on  Cross-Country  Flight  123' 

AIR  DISTURBANCES 

Initial  cross-country  flights  by  the  student  are  usually  made  under  favorable 
weather  conditions,  ordinarily  in  the  early  morning  or  late  evening,  when  the  atmos- 
phere is  calmest.  Bumps  caused  by  heat,  as  explained  in  a  later  chapter  on  meteor- 
ology, manifest  themselves  early  in  the  day  as  close  to  the  ground  as  100  feet;  their 
influence  is  gradually  extended  upward  as  the  morning  progresses  until  they  are  per- 
ceptible at  noon  at  altitudes  up  to  3,000  feet.  Clouds  and  inland  waters  generally 
predict  bumps,  while  over  the  sea  the  air  is  ordinarily  smooth,  although  of  high 
velocity.  Landings  in  strong,  bumpy  winds  are  best  made  with  additional  speed, 
caution  being  exercised  when  nearing  the  ground  in  sheltered  spots  as  wind  eddies 
may  cause  a  sudden  roll  or  a  drop  of  10  feet  or  so. 

LOST  BEARINGS 

Should  something  happen  to  the  compass  and  the  aviator  be  unable  to  get  his 
bearings,  his  wrist  watch  will  be  of  assistance  in  locating  the  points  of  the  compass. 
\Vith  the  hour  hand  pointed  to  the  sun,  the  point  midway  between  the  angle  it  makes 
with  the  numeral  12,  points  to  the  south.  Thus,  at  8  o'clock  in  the  morning,  with  the 
hour  hand  pointed  at  the  sun,  the  point  midway  in  the  angle  formed  by  8  and  12,  i.e. 
10  on  the  watch  dial,  will  point  to  the  south. 

LANDMARKS 

The  principal  landmarks  of  a  map  should  be  firmly  fixed  in  the  aviator's  mind  prior 
to  the  flight,  memorized  if  possible.  Experience  has  shown  that  the  following  features 
are  the  most  useful: 

Towns — These  are  the  best  guides  and  should  be  marked  with  a  circle  or  under- 
lined on  the  map.  A  village  is  sometimes  difficult  of  identification;  location  of  its 
church  and  its  reference  to  the  roads  will  aid  in  placing  it.  If  flying  below  2,000  feet 
altitude  the  aviator  should  not  pass  directly  over  the  town  as  the  heat  from  factory 
chimneys  causes  marked  air  disturbance. 

Railways — Railroad  tracks  are  of  great  assistance.  Tunnels,  bridges  and  cuts  are 
marked  on  the  map  and  aid  in  locating  the  line  to  be  followed  should  the  aviator  mis- 
take a  branch  line  or  siding  for  the  main  route.  It  should  be  remembered  that  the 
track  disappears  when  it  passes  through  a  tunnel. 

Water — Water  courses  and  lakes  are  usually  clearly  defined  and  may  be  seen  at 
some  distance.  Allowances  should  be  made,  however,  for  possible  flooding  of  streams 
after  heavy  rains  which  may  change  their  appearance  as  recorded  on  the  map.  The 
bearing  of  a  river  with  reference  to  the  course  should  be  noted;  following  its  windings 
may  involve  loss  of  time. 

Roads — From  a  height  all  roads  look  very  much  alike  and  are  therefore  not  very 
good  guides.  Main  roads  can  occasionally  be  identified  by  the  paving  and  the  amount 
of  traffic,  and  are  useful  because  they  lead  into  towns.  Telegraph  lines  may  be  expected 
along  them,  which  makes  landing  nearby  dangerous. 

Woods — Small  forests  serve  as  excellent    guides. 

Hills — From  altitudes  of  2,000  feet  and  over,  hills  are  flattened  out  in  appearance 
and  valleys  are  not  clearly  discernible. 

General  Characteristics — The  physical  features  of  the  country  are  very  helpful  to  the  aviator  if  his 
preliminary  study  of  the  map  fixes  in  his  mind  their  relationship  to  each  other.  How  railways  and  streams 
join  or  intersect,  how  they  enter  and  leave  towns,  and  their  relation  to  wooded  areas,  supply  useful 
information.  Dividing  the  course  into  four  progressive  parts  also  aids,  if  the  general  nature  of  each 
sector  is  noted  for  its  chief  distinguishing  characteristics,  whether  water,  woods,  farm  lands,  towns  or 
villages. 

FORCED  LANDINGS 

Engine  failure  is  the  main  cause  of  forced  landings.  As  soon  as  it  is  known  that 
the  failure  is  complete,  the  engine  should  be  switched  off  and  the  gasoline  pipe  closed 
to  lessen  the  danger  of  fire.  The  airplane  is  then  turned  into  the  wind  and  if  the 
ground  directly  beneath  makes  landing  impossible  the  descent  can  be  made  in  a  long 
glide.  While  selection  of  landing  ground  is  not  practical  from  a  recognition  stand- 
point at  altitudes  greater  than  1,000  feet,  entirely  unfavorable  areas  such  as  water, 
marshes  or  forests  may  be  avoided  by  long  glides.  The  radius  of  the  forced  landing  is. 
about  five  times  the  height  at  which  the  airplane  is  flying.  An  aviator  forced  to  land 
from  a  height  of  2,000  feet,  therefore  has  about  10  square  miles  of  land  to  choose  from. 
At  a  height  of  5,000  feet  he  has  selection  in  an  area  of  about  70  miles. 

When  a  forced  landing  has  been  made  the  aviator's  first  thought  should  be  for  his  machine  and  the 
immediate  possibility  of  resuming  flight.  Examination  of  the  engine  is  the  first  step;  it  should  then  be 
determined  how  much,  if  any,  damage  has  been  done  to  the  airplane  structure.  A  telephone  call  to  his 
headquarters  should  then  be  made  and  a  report  given  of  his  location  and  diagnosis  of  the  trouble.  If  the 
damage  requires  staying  where  he  is  for  the  night,  then  the  airplane  should  be  moved  to  some  spot 
sheltered  from  the  wind  and  made  secure. 


124  Practical   Aviation 


TIME  CHECKING 

It  is  difficult  to  estimate  time  while  flying,  yet  checking  by  the  watch  the  time 
when  successive  objects  are  passed  is  an  important  detail  often  overlooked.  The 
tendency  invariably  is  to  expect  the  next  landmark  long  before  it  is  due  and  confusion 
will  arise  in  the  aviator's  mind  unless  time  elapses  are  carefully  checked.  Knowledge 
of  elapsed  time  is  also  valuable  in  steering  a  compass  course  over  the  clouds. 

SELECTING  LANDINGS 

Choosing  a  suitable  field  to  land  in  is  by  no  means  an  easy  task  for  the  novice.  A 
few  primary  rules  governing  selection  will  be  useful. 

It  is  better  to  pick  out  a  group  of  fields  as  the  glide  may  take  the  inexperienced  aviator 
beyond  or  short  of  the  mark. 

Stubble  fields,  brown  in  color  from  a  height,  are  generally  smooth  and,  excepting 
sandy  beaches,  make  the  best  landing  ground. 

Grass  fields,  green  in  appearance,  often  can  be  identified  by  cattle  grazing.  Mounds  may 
be  looked  for  in  grass  land,  so  they  are  therefore  second  choice. 

Cultivated  land  is  ordinarily  fairly  level,  but  landings  made  therein  are  successful  only 
when  pancaked.  A  ploughed  field  is  black  in  appearance,  vegetable  and  corn  fields 
have  a  hue  considerably  darker  than  the  green  of  grass  lands. 

A  field  near  a  town  is  the  best  choice,  as  its  proximity  to  the  source  of  supplies  is  a 
great  convenience.  The  landing  field  selected,  however,  is  preferably  to  windward  of 
the  town,  so  it  will  not  be  necessary  to  rise  over  the  buildings  when  re-starting. 

Telegraph  wires  usually  border  main  roads  and  railways ;  these  wires  cannot  be  seen 
until  the  aviator  is  close  upon  them,  so  nearby  landing  places  are  undesirable. 

When  snow  is  on  the  ground  the  selection  of  a  good  landing  place  is  practically  impos- 
sible; the  frozen  ground,  however,  makes  its  selection  of  less  importance. 

Light  variations  are  important.  Flying  into  the  rays  of  the  sun,  a  slight  haze  appears 
which  distorts  objects.  In  the  late  evening,  too,  the  light  may  be  good  at  the  flying 
altitude,  but  when  descent  is  made  the  ground  appears  much  darker.  Before  landing, 
therefore,  a  wide  circle  should  be  made  until  the  eyes  are  used  to  the  relative  dulness. 

PEGGING  DOWN 

The  airplane  should  be  placed  head  into  the  wind  and  the  tail  lifted  up  and  sup- 
ported at  a  height  which  will  place  the  airplane's  wings  edgewise  to  the  wind.  The 
controls  should  be  locked  and  the  wings  and  fuselage  near  the  tail  pegged  down,  some 
slack  being  left  in  the  rope.  The  propeller,  engine  and  cockpit  should  then  be  covered. 
If  a  strong  wind  is  blowing,  trenches  should  be  dug  for  the  wheels  to  a  depth  of  about 
J4  their  diameter. 

RE-STARTING 

A  minor  trouble  which  does  not  require  calling  a  repair  crew  may  leave  the 
aviator  without  assistance  for  starting,  although  spectators  willing  to  hold  back  the 
airplane  are  generally  more  numerous  than  too  few.  Stones  or  fence  poles  will  serve 
as  chocks  under  the  wheels  if  assistance  is  not  at  hand.  Any  mud  which  may  be  gath- 
ered on  the  wheels  should  be  cleaned  off  as  it  will  be  drawn  to  the  propeller  by  cen- 
trifugal force  and  chip  or  break  it.  Before  starting,  the  ground  over  which  the  machine 
is  to  taxi  should  be  walked  over  carefully  and  any  serious  obstacles  removed.  The 
possibilities  of  dead  wind  in  the  lee  of  buildings  should  be  estimated  and  allowance 
made  to  get  clear  of  these  areas  as  the  airplane  rises.  Small  obstacles,  such  as  hedges, 
may  be  cleared  if  good  taxying  speed  is  acquired  and  the  control  stick  pulled  back 
suddenly.  Getting  rid  of  extra  weight  will  also  aid  the  machine  to  take  the  air  quicker, 
should  there  be  doubt  of  getting  out  of  the  field. 


Practical    Aviation  125 


REVIEW   QUIZ 

Instruction  in  Flying 
First  Flights  and  Gross-Gountry  Flights 

1.  Give  in  simplified  form  the  results  of  manipulating  the  stick  control 
to  its  four  positions  and  the  effect  of  ruddering  to  right  and  left. 

2.  Why  should  the  airplane  be  headed  into  the  wind  at  the  start? 

3.  What  is  the  minimum  taxying  distance  a  beginner  should  allow  before 

rising  from  the  ground? 

4.  State  a  safe  altitude  margin  for  turns,  the  proper  turning  speed  for 

the  novice,  and  give  the  cause  of  side-slips  while  turning. 

5.  In  an  S-turn  how  does  the  landing  spot  selected  serve  as  a  guide? 

6.  Give  three  elementary  rules  of  the  air  which  determine  right  of  way. 

7.  Explain  how  landing  sites  are  identified  and  on  what  portion  of  the 

mark  should  the  airplane  be  brought  to  a  full  stop. 

8.  By  an  example,  state  the  rule  for  gauging  the  distance  allowed  for 

descent  to  the  landing  field. 

9.  Name  the  essential  equipment  and  the  necessary  inspection  required 

of  an  aviator  prior  to  cross-country  flight. 

10.  Define  compass  variation  and  deviation  and  a  method  of  adjusting 

the  compass. 

11.  Lay  off  a  course  by  diagram  for  a  flight  of  100  miles  in  a  direction  of 

12  degrees  east  of  north,  in  an  airplane  with  speed  of  75  m.p.h. 
and  a  wind  blowing  48  degrees  east  of  north  with  a  ground 
velocity  of  25  m.p.h. ;  the  flight  to  be  made  at  2,000  feet  altitude ; 
determine  by  the  diagram  the  proper  steering  direction  to  allow 
for  wind  drift  and  give  the  resultant  compass  bearing. 

12.  Given  the  following  data,  determine  the  radius  of  action  of  the  air- 

plane: Head  wind  blowing  41  m.p.h.;  airplane's  speed,  70  m.p.h.; 
gasoline  capacity,  3%  flight  hours. 

13.  In  what  way  are  cloud  banks  useful  to  the  aviator  flying  above  them? 

14.  Explain  how  a  wrist  watch  is  useful  in  determining  direction  should 

the  compass  be  out  of  commission. 

15.  How  are  towns,  railways  and  water  courses  useful  as  landmarks? 

16.  Why  are  hills  and  roads  poor  guides? 

17.  Give  the  reason  why  checking  the  time  when  successive  objects  are 

passed  is  important. 

18.  What  is  the  difference  between  a  map  contour  and  a  gradient? 

19.  Explain  how  distances  on  a  map  are  determined  by  the  scale  and 

describe  four  ways  of  marking  the  scale. 

20.  From  memory,  sketch  15  conventional  map  signs  denoting  various 

types  of  soil,  communications  and  enclosures. 


126  Practical    Aviation 


CHAPTER    ANALYSIS 

Advanced  Flying 
Aerobatics  and  Night  Flights 

ADVANCED  FLYING: 

(a)  Spiral. 

(b)  Nose  Dive. 

(c)  Spinning  Nose  Dive. 

AEROBATICS: 

(a)  Loop  the  Loop. 

(b)  Flying  Upside  Down. 

(c)  Vertical  Bank. 

(d)  Zooming. 

(e)  Roll  Over. 

(f)  The  Stagger. 

(g)  Spiral  Loop. 

(h)     Immelman  Turn. 

(i)     Flat  Turn. 

(j)     General  Considerations. 

NIGHT  FLYING: 

(a)  Equipment. 

(b)  Preliminary  Instruction. 

(c)  Taking-Off  and  Flying. 

(d)  Landing  at  Night. 

(e)  Lighting  the  Field. 


(  IIAI'TKR  XII 

Advanced  Flying 
Aerobatics  and  Night  Flights 

The  course  of  training  which  leads  to  a  rating  as  Military  Aviator  is 
known  as  advanced  flying.  It  consists  generally  of  effecting  landings  among 
obstacles  and  difficult  turns,  high  altitude-  {lights  and  long  cross-country 
flights;  in  fact,  in  acquiring  great  skill  in  handling  the  airplane.  IJeyond  this 
1  raining  lies  the  acrobacy  of  the  air,  termed  aerobatics,  stunt  flying  which  at 
first  appears  foolhardy  but  has  an  exceptional  value  in  war  where  fast  ma- 
chines are  engaged  in  combat. 

Ascents  to  10,000  feet  or  more  may  be  classed  as  advanced  flying,  although 
these  climbs  present  few  difficulties  and  little  danger.  On  the  assumption 
that  all  aviators  are  plentifully  supplied  with  courage,  climbing  for  the  first 
time  to  high  altitudes  is  largely  a  matter  of  patience. 

A  pertinent  suggestion  to  novices  in  lofty  climbing  is  not  to  imagine  the 
engine  is  stalling  as  height  increases;  the  rarefied  atmosphere  will  require 
less  steep  climb  in  higher  altitudes,  but  that  is  a  matter  for  adjustment,  the 
best  angle-  for  the  particular  machine  being  determined  by  the  aviator's  obser- 
vation of  altimeter  and  watch,  and  their  relation  to  the  airplane's  flight 
efficiency. 

Descent  from  the  first  10,000-foot  flight  is  best  made  slowly,  so  the  aviator 
may  become  accustomed  to  variations  in  air  pressure.  Any  discomfort  in 
breathing  can  usually  be  relieved  by  swallowing  at  frequent  intervals.  It  is 
advisable,  too,  when  the  airplane  has  '*ome  within  1,000  feet  of  the  ground,  to 
circle  once  over  the  flying  field  for  the  purpose  of  refreshing  the  memory  on 
the  appearance  of  the  ground  at  that  height. 

Application  of  the  principles  of  aerobatics  explained  in  this  chapter 
should  be  preceded  in  flight  by  some  hours'  practice  in  climbing  turns  and 
stalling  turns  at  altitudes  of  2,000  to  3,000  feet.  Getting  close  upon  oilier 
airplanes  without  being  seen  is  also  valuable  maneuvering  practice.  Not 
every  pilot  is  successful  in  learning  aerobatics;  comparatively  few,  in  fact, 
are  designated  by  the  instructors  to  master  these  air  evolutions ;  but  the  heady 
man  who  is  physically  fit  takes  to  this  form  of  flying  readily  and  is  fairly 
certain  to  come  out  with  a  whole  skin  if  these  two  primary  rules  are  rigidly 
observed: 

1.  Always  leave  a  wide  altitude  margin  between  the  airplane  and  the 
ground. 

2.  Do  not  effect  too  sudden  changes  of  direction;  straighten  out  grad- 
ually after  diving. 

127 


128 


Practical    Aviation 


(C)     Int.   Film   Svce. 

Figure  96 — An  American  air  squadron  Hying  in  formation  over  the  City  of  New  York 
to  demonstrate  the  absolute  control  of  the  pilots  in  bumpy  air 


Spirals  and  Nose  Dives 


129 


Figure  97 — Descending 
spiral 


Figure  98 — Nose  Dive 


Figure  99 — Spinning 
nose  dive 


SPIRAL 

Descending  spirals,  illustrated  in  Figure  97,  are  made  by  a  continuous  series  of 
banked  turns  in  the  same  direction  with  nose  slightly  down.  The  aileron  control  and 
ruddering  are  governed  by  the  steepness  of  the  descent  desired,  the  controls  ordi- 
narily being  held  steady  until  the  descent  is  accomplished  to  the  designated  point. 
The  aviator  constantly  looks  inward  and  downward  toward  the  center  of  the  circles 
he  describes,  an  occasional  glance  at  the  banking  indicator  serving  to  inform  him  of  the 
accuracy  of  his  turns.  Care  should  be  exercised  that  the  nosing  down  does  not  become 
too  steep,  or  a  spinning  nose  dive  will  result;  too  steep  and  rapid  descent  is  corrected 
by  slightly  pulling  back  the  stick  control. 

!NOSE  DIVE 

The  nose  dive  is  accomplished  by  shutting  off  the  engine  and  pushing  forward  the 
control  stick  suddenly.  The  dive  may  be  made  with  engine  running,  but  this  subjects 
the  airplane  to  severe  strains  and  should  be  avoided.  First  dives  should  not  be  as 
steep  as  that  shown  in  Figure  98,  and  the  novice  should  learn  the  trick  far  above  the 
ground.  At  not  less  than  1,000  feet  altitude  the  airplane  should  be  straightened  out; 
this  is  accomplished  by  a  firm  but  gradual  backward  pull  on  the  control  stick.  When 
the  air  speed  indicator  registers  low  flying  speed  the  control  should  be  centered  and 
the  engine  switched  on. 

SPINNING  NOSE  DIVE 

From  the  spiral  it  is  very  easy  to  go  into  a  spinning  nose  dive,  illustrated  in  Figure 
99.  While  it  is  a  recognized  maneuver  of  air  tactics,  the  spinning  nose  dive  is  generally 
the  result  of  slowing  down  in  the  spiral,  which  then  becomes  too  steep,  the  tail  planes 
acting,  so  to  speak,  as  a  vertical  rudder,  and  the  rudder  functioning  as  an  elevator. 
The  revolutions  and  fall  of  the  machine  are  very  fast;  the  aviator  should  avoid  looking 
at  the  ground  while  in  the  spin. 

To  get  out  of  a  nose  spin,  both  feet  should  be  evenly  pressed  against  the  foot  bar 
until  it  is  held  straightened;  this  evens  up  the  rudder  and  stops  the  spinning.  The 
control  stick  is  then  brought  to  center  and  back;  then  pushed  forward.  A  steady  pull 
back,  and  the  airplane  levels  out.  The  engine  throttle  is  then  opened  and  the  flight 
parallel  to  the  ground  continued. 


130 


Practical    Aviation 


Figure  100 — Looping  the  loop 


Figure  101 — Flying  upside  down 


LOOP  THE  LOOP 

Looping  the  loop  is  a  comparatively  simple  and  effective  air  evolution. 
A  height  greater  than  3,000  feet  should  be  selected  and  the  descent  begun  at 
a  more  gradual  angle  than  employed  in  the  nose  dive.  When,  with  the  aid 
of  the  motor,  a  speed  of  75  miles  per  hour,  or  better,  has  been  attained,  a  firm 
backward  pull  on  the  control  stick  causes  the  airplane  to  rise  and  turn  over. 
The  backward  pull  should  begin  at  point  1,  Figure  100,  and  the  stick  be  all 
the  way  back  at  point  2.  When  the  airplane  is  upside  down  and  the  ground 
visible  below,  the  motor  may  be  cut  off  (point  3,  Figure  100),  in  which  case 
the  airplane  will  describe  the  smaller  loop  along  course  A.  The  stick  is  held 
back  steady  until  point  4  is  reached,  Avhen  it  is  steadily  moved  forward  to 
center,  the  motor  being  switched  on  at  point  5.  The  loop  can  be  made  with 
the  engine  on,  but  the  recovery  will  not  be  as  quick,  the  airplane  following 
the  course  B. 

Special  cautions — Control  movements  in  looping  should  be  steady  and 
firm;  jerkiness  may  produce  dangerous  stresses  and  lead  to  possible  collapse. 

The  aviator's  safety  belt  should  be  securely  adjusted  and  seat  cushions 
removed. 

Looping  is  best  done  against  the  wind. 


FLYING  UPSIDE  DOWN 

This  maneuver  is  executed  the  same  as  looping  up  to  point  6,  Figure  101. 
Here  the  engine  may  or  may  not  be  throttled  down.  If  the  engine  speed  is 
reduced  the  steeper  course  D  must  be  taken,  as  there  is  danger  of  stalling  at 
a  lesser  angle.  With  the  engine  on  full,  the  stick  control  is  pushed  forward 
to  center,  at  point  6,  the  airplane  then  flying  upside  down  in  the  approximate 
course  C. 


Vertical  Bank,  Zooming,  Roll  Over  and  Stagger 


131 


Figure  102   (Upper} — Vertical  bank     Figure  104 — The  roll  over,  also  known  as  the  barrel 
Figure  103  (Lower} — Zooming 

VERTICAL  BANK 

Banking  at  angles  greater  than  45  degrees  is  known  as  vertical  banking.  No  par- 
ticular difficulties  are  encountered  in  these  exaggerated  turns,  but  the  aviator  must 
become  accustomed  to  the  reverse  order  of  control  functions  while  in  this  position. 
See  Figure  102. 

The  vertical  bank  is  accomplished  by  pushing  both  aileron  and  rudder  controls  far 
over  in  the  desired  direction.  Once  the  airplane  is  on-  its  side,  the  tail  elevating  planes 
act  as  a  rudder  and  the  rudder's  function  is  that  of  the  elevator. 

The  next  step  after  banking  is  to  level  the  airplane  horizontally  with  the  horizon. 
Pushing  the  rudder  liar  with  the  foot  which  is  uppermost  will  raise  the  nose,  and  rud- 
dering from  the  bottom  will  lower  the  nose.  To  turn  the  airplane  while  on  its  side  the 
control  stick  is  eased  back  slightly  in  the  direction  opposite  its  position  for  the  original 
banking. 

Coming  out  of  the  vertical  bank,  the  stick  control  is  pushed  full  over  to  the  opposite 
side,  and  as  the  airplane  reaches  a  position  nearly  horizontal,  opposite  ruddering  is 
given  to  the  degree  necessary,  the  stick  control  then  being  centered  a  trifle  forward. 
The  aviator  should  remember  that  the  rudder  is  not  to  be  thrown  over  until  the 
machine  is  near  the  horizontal,  for  its  action  has  changed;  it  is  acting  as  an  elevator 
while  the  airplane  is  on  its  side,  and  raising  the  nose  may  result  in  a  stall. 

ZOOMING 

This  consists  of  a  sudden  upward  rise  or  jump  while  flying  at  high  speed.  It  is 
illustrated  in  Figure  103.  The  upward  rise  is  obtained  by  pulling  the  stick  control  back 
suddenly.  The  machine's  climb  ends  with  the  stalling  point,  when  the  control  stick 
must  be  pushed  forward  again.  The  stalling  point  is  best  made  known  to  the  aviator 
by  the  sloppy  feeling  of  the  controls;  the  air  speed  indicator  may  also  be  consulted, 
but  it  is  not  so  reliable  by  reason  of  the  lag.  Caution  must  be  exercised  in  zooming 
that  the  control  is  pushed  forward  and  speed  regained  before  the  airplane  stalls,  or  a 
dangerous  tail  spin  may  result. 

ROLL  OVER 

A  very  effective  and  comparatively  easy  evolution  is  rolling,  also  known  as  the 
barrel,  or  roll  over.  The  airplane  at  high  speed  is  made  to  trace  an  air  course  like  a 
screw  thread,  as  illustrated  in  Figure  104. 

The  roll  over  may  be  begun  at  a  speed  of  about  95  miles  per  hour,  the  control 
stick  being  thrown  away  over  to  the  left  (or  right)  throwing  the  left  aileron  up  and 
the  opposite  aileron  down;  the  feet  are  kept  still  on  the  rudder  bar. 

Coming  out  of  the  roll  is  accomplished  by  bringing  the  control  stick  back  to  center 
just  as  the  airplane  levels  out  at  the  top  of  a  turn. 

THE  STAGGER 

A  veritable  see-saw  may  be  made  out  of  the  roll  over  by  giving  the  stick  control 
a  circular  motion  and  alternately  pushing  right  and  left  on  the  rudder  bar  in  synchron- 
ism as  the  stick  successively  comes  round  right  and  left. 


132 


Practical    Aviation 


Figure   W5—The   spiral  loop 


Figure  106 — The  Immclman  turn 


SPIRAL  LOOP 

This  is  a  difficult  evolution,  but  it  has  the  special  advantage  of  bringing  the  aviator 
back  to  approximately  the  same  position  from  which  he  started  and  headed  in  the  same 
direction.  The  course  of  the  airplane  is  shown  in  Figure  105. 

The  beginning  is  the  same  as  for  looping;  when  the  machine,  upside  down,  reaches 
the  top  of  its  loop,  however,  the  motor  is  cut  out  and  the  control  stick  pushed  sharply 
forward,  the  rudder  being  kicked  sharply  left  (or  right).  The  airplane  begins  to  fall 
on  its  back  and  spin  slowly  around;  at  the  half-turn,  the  rudder  is  centered  and  the 
stick  pulled  back  until  the  machine  straightens  out.  The  engine  is  then  switched  on  and 
the  level  flight  continued. 

IMMELMAN  TURN 

The  course  of  this  famous  German  evolution  is  shown  in  Figure  106.  It  consists 
of  turning  the  airplane  over  sideways  as  it  begins  to  zoom,  and  righting  it  so  it  comes, 
down  in  the  opposite  direction.  It  can  be  done  with  engine  on  or  off. 

The  evolution  is  begun  just  like  the  loop,  the  control  stick  being  pulled  back  two- 
thirds  of  the  way  for  the  steep  ascent.  When  the  machine  is  at  the  vertical  position, 
the  foot  bar  is  pushed  over  left  (or  right)  throwing  the  rudder  and  causing  the  airplane 
to  describe  an  inverted  U  to  the  left.  As  it  noses  down  the  control  stick  is  pulled 
back  the  remaining  one-third  and  the  elevating  planes  straighten  out  the  airplane 
parallel  to  the  ground. 

FLAT  TURN 

A  useful  maneuver  in  air  fighting  is  the  flat  turn,  which  enables  the  aviator  to  make 
a  quick  sweep  to  the  side.  This  is  accomplished  by  cutting  off  the  engine  for  an  instant, 
kicking  the  rudder  bar  full  over,  then  centering  it.  The  side  sweep  is  through  an  arc 
of  about  90  degrees;  most  of  the  flying  speed  is  lost  in  the  turn.  Centering  the  rudder 
quickly  after  throwing  the  bar  over  prevents  the  airplane  from  entering  into  a  spin. 


GENERAL  CONSIDERATIONS 

Height — The  aviator  who  engages  in  aerobatics  cannot  be  cautioned  too  strongly 
about  allowing  a  good  altitude  margin.  A  miscalculation  of  speed  or  distance,  or 
engine  failure,  has  many  times  resulted  in  a  fatality  when  the  machine  was  too  close 
to  the  earth. 

Bumps — In  aerobatics  it  is  a  common  experience  for  the  aviator  to  encounter 
bumps  caused  by  the  air  disturbances  created  by  his  own  machine;  these  are  not  serious 
and  should  give  no  cause  for  alarm  when  encountered. 

Lost  Control — A  general  rule  for  safety  when  the  airplane  gets  out  of  control  is 
to  throttle  down  or  cut  off  the  engine.  If  at  a  good  altitude  the  nose  dive  should  then 
be  attempted.  An  unexpected  spin  should  not  cause  confusion,  because  if  the  rudder 
is  held  firmly  in  the  center  position,  with  sufficient  altitude  the  airplane  will  right  itself. 


Night  Flying 


133 


From  painting  by  Lieut.  Farre 

lights  and  the  method  of  lighting  the  landing  field 
Bombing  airplanes  returning  at  night  from  an  air  raid,  illustrating  the  use  of  search- 

NIGHT    FLYING 

Nearly  all  bombing  raids  and  air  offensives  are  conducted  at  night ;  flying 
after  dark  is  not  particularly  dangerous  under  instruction  conditions,  but  con- 
siderable skill  is  required  for  a  night  raid  over  hostile  territory. 

EQUIPMENT 

The  airplanes  used  are  generally  those  of  marked  stability,  thus  relieving  the  pilot 
of  the  mental  strain  of  control;  for  this  reason,  also,  aviators  ordinarily  make  a  night 
flight  in  machines  with  which  they  have  become  thoroughly  familiar  in  daylight.  The 
figures  on  instruments  are  treated  with  luminous  paint  and  two  shaded  electric  lights 
are  ordinarily  provided  to  illuminate  the  dashboard.  Another  electric  light  is  usually 
placed  on  the  floor  of  the  cockpit.  Flares  for  use  in  case  of  forced  landing  are 
included;  these  are  of  the  parachute  type  and  include  in  the  equipment  an  electric 
launching  tube.  Navigation  lights  are  placed  on  the  wing  tips,  red  on  the  left,  green 
on  the  right,  and  a  searchlight  is  generally  included  to  light  up  the  ground  when 
landing.  Electric  current  is  principally  used  for  these  searchlights,  a  yellow  metallic 
mirror  reflector  throwing  a  ray  which  best  penetrates  mist.  The  flares  have  the 
advantage  of  illuminating  a  mile  or  so  area  for  about  four  minutes,  whereas  the 
searchlight  rays  are  confined  to  a  small  radius;  both  are  usually  carried,  however.  An- 
other lighting  scheme  provides  a  row  of  electric  lights  with  reflectors,  placed  under 
the  leading  edge  of  the  lower  wings.  The  propeller  and  bright  metal  parts  are 
painted  black  so  as  not  to  dazzle  the  aviator's  eyes. 

PRELIMINARY  INSTRUCTION 

Practice  for  night  flying  broadly  includes  a  daylight  rehearsal  of  exactly  how 
the  airplane  will  fly  at  night.  Flying  by  the  instruments  alone,  without  guiding  by 
the  horizon,  should  be  accomplished;  slow  glides  should  be  practiced;  small  side- 
slips and  quick  recoveries  should  be  effected;  slow  landings  and  turning  with  the 
instruments  as  the  sole  guide  perfected,  and  the  pilot  should  become  accustomed  to 
the  sound  or  "sing"  of  wires  at  different  speeds  and  varying  conditions. 

An  aviator's  fitness  for  night  flying  is  generally  gauged  by  his  success  in  making 


134  Practical    Aviation 


a  half-dozen  or  more  solo  landings  in  the  darkness;  night  instruction  by  dual  control 
is  seldom  given. 

An  essential  portion  of  his  knowledge  is  thorough  familiarity  with  the  country 
over  which  he  is  to  fly  at  night  and  full  acquaintance  with  the  airdrome  in  which 
he  is  to  land. 

TAKING-OFF  AND  FLYING 

As  the  airplane  is  wheeled  into  position  the  aviator  carefully  notes  the  lighting 
and  layout  of  the  landing  ground  in  the  airdrome.  The  landing  is  usually  indicated 
by  a  chain  of  lights  in  the  form  of  an  L,  those  at  the  lower  end  marking  the  point 
before  which  a  full  stop  must  be  effected.  The  lighting  is  arranged  so  the  wind 
blows  up  the  long  arm  of  the  L,  and  the  machine  is  faced  into  the  wind  for  the 
start  at  the  end,  or  top,  of  the  letter.  The  number  and  spacing  of  the  lights  is  fixed 
by  the  commanding  officer;  these  should  be  counted  by  the  pilot  and  an  estimate 
made  of  the  distance  allowed  for  taking-off;  obstacles  should  be  noted,  for  the  landing 
on  the  return  is  to  be  made  on  the  same  ground.  Taking-off  at  night  has  one  impor- 
tant difference  from  daylight  flying;  at  night  the  airplane  is  allowed,  so  to  speak,  to 
rise  from  the  ground  itself,  the  instant  when  it  becomes  difficult  to  hold  the  machine 
down  being  the  proper  time  for  the  take-off. 

The  rigging  for  night  flying  is  also  preferably  changed,  so  that  with  the  control 
stick  neutral  the  airplane  is  in  a  position  for  slight  climb;  this  adjustment  assures 
medium  and  uniform  speed,  which  is  further  provided  for  by  adjusting  the  engine 
throttle  so  level  flight  is  obtained  when  it  is  half  open.  The  take-off  is,  as  already 
explained,  made  into  the  wind. 

Night  pupils  should  remain  within  gliding  distance  of  the  airdrome  and  avoid 
clouds  which  obscure  the  ground  lighting.  Flights  made  on  moonlight  nights  permit 
the  aviator  to  see  his  landing  field  plainly,  but  it  must  be  remembered  that  the  airplane 
is  quickly  lost  to  the  view  of  those  on  the  ground.  Railways  cannot  be  identified 
easily,  even  under  perfect  conditions,  but  the  white  smoke  from  a  train  on  clear 
moonlit  nights  and  villages  and  towns  are  easily  discerned,  and  roads  recognized  at 
7;000  feet.  On  moonless  nights  only  lights  can  be  seen  from  5,000  feet;  rivers,  rail- 
ways and  roads  are  not  distinguishable,  but  the  airdrome  flares  are  easily  recognized. 
If  other  pupils  are  in  the  air,  the  red  and  green  navigation  lights  are  lit  at  2,000  feet. 

LANDING  AT  NIGHT 

The  straight  glide  is  the  only  type  of  landing  to  be  attempted  by  the  student 
aviator;  the  glide  should  begin  at  least  a  mile  away  with  the  engine  turning  over 
slowly;  when  within  less  than  fifty  feet  of  the  ground  the  engine  should  be  switched  off 
and  the  airplane  allowed  to  come  down  of  itself;  that  is,  the  nose  should  not  be  put 
down. 

Signals  for  landing  are  arranged  beforehand.  By  them  the  aviator  recognizes 
his  own  airdrome,  for  when  over  his  field  and  ready  to  descend  he  fires  the  prescribed 
colored  light,  which  is  answered  from  the  ground  by  a  light  of  the  color  prearranged. 
He  then  gives  the  landing  signal  and  the  flares  are  lit  for  his  descent. 

The  searchlight,  if  the  airplane  is  equipped  with  one,  is  sometimes  switched  on 
at  about  1,500  feet  and  the  ground  searched  for  the  landing  field.  A  pilot  flying  alone 
will  find  its  manipulation  difficult,  so  at  a  low  altitude  it  is  switched  off  and  a  flare 
dropped  over  the  field.  If  an  observer  is  carried  the  searchlight  is  left  to  his  hands. 

LIGHTING  THE   FIELD 

Proper  lighting  of  a  landing  field  is  a  matter  of  extreme  importance.  There  are 
various  types  and  lighting  arrangements,  but  usually  gasoline  flares  or  flame  arc 
lamps  are  used,  laid  out  in  L-form  and  aided  by  searchlights  which  point  into  the 
wind,  or  away  from  the  eyes  of  the  aviator  who  is  landing.  When  the  searchlights 
are  used  they  serve  to  light  up  the  strip  of  ground  which  serves  as  a  runway  for 
the  airplane. 

Twin,  parallel  and  triangular  light  arrangements  have  been  proposed  and  used, 
as  well  as  concentric  light  circles.  The  arrangement  most  in  favor  is  the  L,  however, 
which  is  laid  out  this  way: 

S  *  *  *  *  * 

Land  here >•  -< Wind 

S  * 

In  the  above  diagram  S.  S.  are  the  searchlights,  and  the  asterisks  the  flares, 
placed  a  fixed  distance  apart  and  in  the  number  specified  by  the  commanding  officer. 
The  short  arm,  or  bottom,  of  the  L,  designates  the  point  where  the  airplane  must  be 
brought  to  a  full  stop.  Should  the  airplane  not  reach  the  ground  before  half  the 
length  of  the  long  arm  has  been  traversed,  the  aviator  should  not  attempt  to  land, 
but  should  switch  on  his  engine  and  rise  for  another  circuit. 


Practical    Aviation  135 


REVIEW  QUIZ 

Advanced  Flying 
Aerobatics  and  Night  Flights 

1.  Why  is  it  advisable  to  make  a  slow  descent  the  first  time  a  height  of 

10,000  feet  is  attained? 

2.  Give  two  primary  rules  to  be  observed  when  learning  aerobatics. 

3.  State  the  direction  for  an  aviator  to  look  while  making  a  descending 

spiral. 

4.  How  should  the  control  stick  be  handled  in  straightening  out  of  a 

nose  dive? 

5.  Give  the  reason  why  a  nose  dive  sometimes  becomes  a  spinning  nose 

dive  and  explain  the  action  of  the  control  surfaces  while  in  the 
latter. 

6.  What  are  the  control  operations  required  to  bring  an  airplane  out 

of  a  nose  spin? 

7.  In  looping  the  loop,  what  is  the  effect  on  the  descending  flight  path 

if  the  motor  is  cut  off  when  the  airplane  is  upside  down? 

8.  What  special  manner  of  handling  controls  is  required  when  looping? 

Give  the  reason. 

9.  Explain  how  the  vertical  bank  is  accomplished  and  how  the  action 

of  controls  is  changed. 

10.  How  is  the  airplane  leveled  with  the  horizon  when  in  a  vertical  bank? 

11.  Describe  the  evolution  known  as  zooming  and  state  the  indications 

which  announce  the  end  of  the  climb. 

12.  What  action  of  controls  starts  the  airplane  on  the  barrel,  or  roll  over, 

and  how  is  the  machine  brought  out  of  the  evolution? 

13.  Explain  the  action  of  the  controls  which  cause  the  airplane  to  stagger 

or  see-saw. 

14.  Describe  the  successive  movements  of  a  spiral  loop  and  the  manipu- 

lation of  the  controls. 

15.  How  does  the  spiral  loop  differ  from  the  Immelman  turn? 

16.  Describe  the  Immelman  turn  and  how  the  controls  are  handled. 

17.  What  control  manipulations  are  required  to  make  a  flat  turn? 

18.  Give  a  general  rule  for  safety  when  an  airplane  gets  out  of  control. 

19.  What  details  should  be  mentally  noted  by  the  aviator  about  to  begin 

a  night  flight? 

20.  State  in  detail  the  nature  of  the  glide  and  landing  a  student  should 

make  at  night  and  the  relation  of  the  field  lighting  to  his  landing. 


136  Practical    Aviation 


CHAPTER  ANALYSIS 

Meteorology  for  the  Airman 

CHARACTERISTICS  OF  THE  AIR: 

(a)  Composition  of  the  Atmosphere. 

(b)  Atmospheric  Pressure. 

(c)  Measure  of  Pressure. 

(d)  Pressure  Areas. 

(e)  Cyclone  Area. 

(f)  Anti-cyclone  Area. 

(g)  Secondary  Depressions, 
(h)  The  Wedge. 

(i)  Line  Squalls, 

(j)  Beaufort  Scale. 

WIND  CONDITIONS  WHICH  AFFECT  AVIATION 

(a)  Wind  Distribution. 

(b)  Aerial  Fountain. 

(c)  Aerial  Cataract. 

(d)  Aerial  Cascade. 

(e)  Aerial  Breakers. 

(f)  Vertical  Wind  Eddies. 

(g)  Wind  Layers. 
(h)  Wind  Billows. 

(i)      Wind  Gusts  and  Eddies. 
(j)      Aerial  Torrents. 

CLOUDS  AND  THEIR  SIGNIFICANCE: 

(a)  Classification  of  Clouds. 

(b)  General  Observation. 


CHAPTER  XIII 

Meteorology  for  the  Airman 

In  many  ways  the  air  is  comparable  to  the  sea ;  in  fact,  in  a  large  portion 
of  the  study  of  the  basic  principles  of  aerodynamics  the  action  of  the  sea  is 
used  as  an  analogy.  The  professional  pilot  of  water  craft  who  lacks  knowl- 
edge of  the  ocean  is  unheard  of ;  and  so  must  it  be  with  the  military  aviator's 
knowledge  of  the  air.  Successful  flying  over  long  periods  is  largely  due  to  an 
aviator's  understanding  of  the  air  and  its  vagaries ;  in  fact,  where  this 
knowledge  does  not  exist,  continued  success  is  entirely  a  matter  of  luck. 
Some  grasp  of  the  elementary  principles  of  meteorology  is  therefore  essential. 
It  may  be  gained  by  experience,  but  this  method  has  more  than  once  led  to 
fatal  misconceptions.  Theoretical  instruction,  through  which  ability  is 
acquired  to  apply  the  scientific  laws  of  weather  forecasting,  is  a  safeguard 
well  worth  the  time  spent  in  acquiring  it. 

Flying  over  hostile  territory  in  war  time  requires  the  aviator  to  ascend 
under  all  types  of  weather  conditions.  By  thorough  acquaintance  with 
meteorological  factors  which  bear  on  aviation,  or  aerography,  as  it  is  aca- 
demically called,  the  pilot  may  know  at  a  glance  what  the  behavior  of  his 
machine  is  likely  to  be,  and  will  not  be  surprised  into  falling  out  of  control 
through  ignorance. 

The  best  weather  for  flying  is  obtainable  on  a  calm,  clear  day,  when 
eddies  or  vertical  currents  are  not  likely  to  be  encountered.  A  strong  gale 
is  about  the  only  condition  that  makes  flight  impossible  to  the  modern  air- 
plane, although  fog  is  a  considerable  handicap  to  military  flying,  by  reason 
of  the  poor  chances  for  proper  observation. 

A  ground  haze,  low  lying  clouds,  and  location  of  the  sun  dead  ahead, 
also  impede  useful  military  flight,  as  do  detached  clouds;  but  none  of  these 
prevent  the  aviator  going  aloft.  Air  eddies  and  ascending  or  descending 
currents,  too,  are  seldom  so  violent  that  flying  is  seriously  interfered  with. 
For  students  engaged  in  first  flights,  the  early  morning  and  evening  are  the 
most  suitable  times,  for  it  is  then  that  the  air  is  calmest.  In  the  United  States, 
winds  from  the  east  and  southeast  carry  with  them  less  "bumps"  and  are 
most  favorable. 

137 


138  Practical    Aviation 


CHARACTERISTICS  OF  THE  AIR 

COMPOSITION  OF  THE  ATMOSPHERE 

Air  is  a  gaseous  body,  which,  like  water,  seeks  the  level  where  lowest 
pressure  exists.  It  is  1,600  times  lighter  than  water,  but  it  is  at  least  50 
miles  deep,  and  since  one-half  of  its  weight  is  below  3  miles  altitude,  its 
weight  or  pressure  at  the  earth  is  considerable.  Its  constituents  are :  nitrogen, 
79  per  cent.;  hydrogen,  20  per  cent.;  argon,  1  per  cent. 

ATMOSPHERIC  PRESSURE 

The  weight  of  air  on  a  given  spot  is  atmospheric  pressure.  The  longer 
the  column  of  air  above  the  place,  and  the  greater  the  density  of  the  air,  the 
greater  will  be  the  pressure  at  the  bottom  of  the  column. 

Pressure  is  variable,  however.  The  temperature  of  the  air  usually  decreases  with 
height  at  a  rate  of  about  one  degree  for  every  300  feet.  This  rule  is  not  an  absolute 
one,  since  temperature  varies  with  locality  and  season  of  year,  but  is  useful  as  a 
general  guide.  Density  of  the  air  is  affected  by  temperature,  due  to  the  expansion  of 
heated  air  and  contraction  of  cold;  density  is  also  affected  by  pressure,  for  the  higher 
the  air  column  the  greater  the  air  contained  in  a  given  space  at  the  bottom. 

Air  at  rest  is  given  motion  by  change  in  temperature  at  the  earth.  For  example, 
heat  from  the  sun's  rays  is  not  absorbed  uniformly,  bare  earth  heating  more  rapidly 
than  portions  covered  by  trees  and  grass.  Over  the  bare  spot  the  heated  column  of  air 
will  rise  by  expansion,  and  as  it  rises  the  pressure  there  will  be  diminished,  whereupon 
the  cooler  surrounding  air  will  rush  into  the  vacated  space.  As  the  operation  is 
repeated  the  air  motion  increases.  Thus  elevations  and  depressions  are  formed,  or, 
as  they  are  termed  in  meteorology:  HIGH  PRESSURE  AREAS  and  LOW  PRES- 
SURE AREAS. 

MEASURE  OF  PRESSURE 

The  barometer  is  the  instrument  used  to  measure  air  pressure.  It  is  measured  by 
the  height,  in  inches,  of  a  column  of  mercury  necessary  to  balance  it.  At  a  fixed  time 
each  day  atmospheric  pressures  taken  at  various  stations  scattered  over  the  country  are 
telegraphed  to  the  meteorological  office  and  a  weather  map  is  made  from  those  reports. 
Such  a  map  is  illustrated  in  Figure  107. 

By  joining  places  which  register  the  same  barometric  pressure,  lines  are  formed 
similar  to  map  contour  lines  and  known  as  isobars. 

PRESSURE  AREAS 

All  places  on  any  line  (isobar)  have  the  same  atmospheric  pressure;  where  little 
difference  of  pressure  exists  at  places  close  together,  the  isobars  will  be  close  together, 
and  vice  versa.  The  air  forced  from  high  pressure  to  an  area  of  lower  pressure  does  not 
follow  a  straight  line,  but  takes  a  spiralling  course  in  a  direction  more  nearly  parallel 
to  the  isobars  than  at  right  angles.  This  is  due  to  the  irregularities  of  the  earth's 
surface  and  the  revolution  of  the  earth  on  its  axis. 

Pressure  areas,  which  usually  have  a  diameter  of  hundreds  of  miles,  do  not  remain 
in  the  same  position,  examination  of  U.  S.  weather  maps  for  successive  days  showing 
that  they  ordinarily  move  in  a  general  easterly  direction  and  occasionally  north  and 
south,  but  westward  only  in  hurricanes. 

An  unusually  small  pressure  area  indicates  a  cyclone  area  and  sudden  violent 
changes  in  weather  may  be  looked  for.  In  a  high  pressure  region,  or  anti-cyclone, 
the  weather  to  be  expected  and  the  indications  are  almost  the  reverse. 

Since  the  winds  flow  spirally  about  the  pressure  areas,  the  isobars  on  the  weather 
map  furnish  the  aviator  information  as  to  the  general  direction  of  the  wind,  knowledge 
which  is  extremely  valuable  if  a  cross-country  flight  is  contemplated. 

CYCLONE  (LOW  PRESSURE  AREA) 

The  winds  blow  anti-clockwise  about  the  center  of  pressure  (clockwise  in  the 
southern  hemisphere).  The  barometer  falls  with  the  approach  of  the  cyclone,  begin- 
ning to  rise  again  after  the  center  of  the  area  has  passed.  The  front  of  the  depressed 
area  usually  holds  rain  or  cloudiness,  the  rear  cooler  weather  and  clearing. 

ANTI-CYCLONE    (HIGH   PRESSURE   AREA) 

An  anti-cyclone  has  no  general  direction  of  motion,  in  fact  it  is  frequently  station- 
ary for  days.  The  winds  spiral  clockwise  from  the  center  and  are  very  light.  Almost 
any  type  of  weather  may  be  expected  except  heavy  winds.  Ordinarily,  the  weather 
is  fine,  but  in  cold  weather  fog  and  low  lying  clouds  are  frequent,  and  rain  occasional. 


Characteristics  of  the  Air 


139 

\ 


PC'-/,\  ^•••^;-fU4i 

;i,^  h~\tf      A.-V;  V:. 


Figure  107 — Meteorological  map  showing  atmospheric  pressures 

SECONDARY   DEPRESSIONS 

Irregularities  in  the  form  of  indentations  in  the  isobars  frequently  appear  in  a 
cyclone  area.  These  secondary  formations  may  or  may  not  be  well  defined;  if  marked, 
the  winds  may  become  very  strong  and  the  weather  bad.  In  front  of  the  secondary 
the  weather  is  similar  to  the  cyclone;  between  the  secondary  and  main  depression  the 
winds  are  light,  but  very  strong  on  the  side  furthest  from  the  center  of  the  cyclone. 

THE  WEDGE 

When  a  series  of  cyclones  pass  across  country  in  continuous  succession,  V-shaped 
isobars  appear  between  cyclones.  These  indicate  fine  clear  weather,  but  of  short  dura- 
tion, as  another  cyclone  is  approaching. 

LINE  SQUALLS 

As  the  center  of  a  cyclone  passes  line  squalls  often  appear.  They  are  usually  very 
narrow  but  often  500  miles  in  length,  are  very  sudden  and  violent  and,  traveling 
approximately  at  a  right  angle  to  their  length  are  very  dangerous  to  airmen.  The 
barometer  shows  a  small  sudden  rise,  and  a  fall  in  temperature  is  noticeable;  often 
heavy  rain  and  hail  set  in,  and,  occasionally,  thunder.  These  squalls  seldom  give  any 
warning  and  are  therefore  particularly  dangerous. 

BEAUFORT  SCALE 

Wind  strength  is  generally  expressed  as  velocity  in  miles  per  hour.  For  con- 
venience winds  are  divided  into  12  groups  or  classifications,  a  system  known  as  the 
Beaufort  scale. 

BEAUFORT    SCALE 


Division 

Nautical 

Description 

Division 

Nautical 

Description 

Number 

m.  p.  h. 

of  Wind 

Number 

m.  p.  h. 

of  Wind 

0 

Less   than    1 

Calm 

7 

28—33 

High    wind 

1 

1—  3 

Light   air 

8 

34—40 

Gales 

2 

4—  6 

Slight  breezes 

9 

41—47 

Strong  gales 

3 

7—10 

Gentle  breezes 

10 

48—55 

Whole  gale 

4 

11—16 

Moderate    breezes 

11 

56—65 

Storm 

5 

17—21 

Fresh    breezes 

12 

Above  65 

Hurricane 

6 

22—27    ' 

Strong  breezes 

140 


Practical    Aviation 


Wind  Columns,  Eddies  and  Gusts  141 

WIND  CONDITIONS  WHICH  AFFECT  AVIATION 

WIND  DISTRIBUTION 

The  aviator  does  not  need  to  study  the  cause  of  wind,  but  he  should 
know  something  of  its  distribution.  Wind  is  stronger  by  day  than  by  night  at 
the  earth's  surface;  its  average  velocity  in  the  United  States  is  11  miles  per 
hour,  normally  increasing  with  altitude  up  to  1,000  feet,  above  which  height  it 
"veers,"  or  goes  round  in  a  clockwise  direction. 

The  following  condensed  scale  is  useful  for  calculating  wind  problems: 
At  1,000  feet  wind  velocity  increases  1$4   times,  with   10  degree  veering. 
At  2,000  feet  velocity  nearly  doubles  and  wind  veering  is  15  degrees. 
Above  3,000   feet  velocity  is  double  and   there   is   practically   no   further   increase   and 
veering  is  constant  at  20  degrees. 

AERIAL  FOUNTAIN 

A  rising  current  of  atmosphere  encountered  over  barren  land  and  conical  hills  in 
warm  weather,  the  air  column  rising  because  it  is  heated  beyond  the  temperature  of  the 
surrounding  air.  These  fountains  are  not  ordinarily  dangerous  but  the  rate  of  ascent 
has  been  known  to  reach  a  velocity  of  25  feet  per  second.  The  airplane  will  rise  invol- 
untarily if  caught  squarely  by  one  of  these  columns,  dropping  as  it  emerges.  Wing 
tips  will  be  tilted  if  the  aerial  fountain  is  grazed.  See  Figure  108. 

AERIAL  CATARACT 

Descending  cold  air  causes  a  current  which  takes  two  forms  (a)  the  reverse  of  the 
aerial  fountain  with  opposite  effect  on  airplanes,  and  dangerous  only  in  thunder  storms; 
(b)  surface  cataracts  developed  by  steep  barren  slopes  of  earth.  The  action  of  the 
surface  cataract  is  shown  in  Figure  109.  Landing  should  never  be  attempted  in  a 
surface  cataract. 

AERIAL  CASCADE 

The  bounding  air  at  the  bottom  of  a  steep  fall  over  an  earth  contour  is  similar  to 
the  result  with  a  water  cascade.  Eddies  of  a  treacherous  character  are  set  up,  and 
counter  currents,  above  which  the  aviator  must  remain  for  safety. 

AERIAL  BREAKERS 

Strong  cross  currents  form  choppy  winds  with  action  similar  to  ocean  breakers. 
These  are  generally  heralded  by  corrugated  clouds  and  are  to  be  noted  as  difficult  of 
navigation  by  air  pilots. 

VERTICAL  WIND  EDDIES 

Below  the  crests  of  hills  wind  eddies  form,  which  describe  circles  in  the  vertical 
plane.  See  Figure  110.  Should  the  aviator  be  caught  in  the  pocket  under  a  hill  the 
airplane  should  be  headed  in  and  a  landing  made  parallel  to  the  side  of  the  hill. 

WIND  LAYERS 

Wind  will  very  often  be  found  blowing  in  different  directions  and  velocities  at 
different  heights!  Although  horizontal,  passing  from  one  layer  to  another  of  different 
speed  and  different  direction  momentarily  changes  the  buoyancy  of  the  airplane,  causing 
the  machine  to  rise  or  fall.  Turbulent  motion  and  a  few  bumps  will  only  be  expe- 
rienced, and  wind  layers  are  therefore  not  ordinarily  dangerous. 

WIND  BILLOWS 

These  are  horizontal  billows  similar  to  ocean  waves  and  occur  at  the  surface 
between  wind  layers;  rough  going,  not  necessarily  dangerous,  results. 

WIND  GUSTS  AND  EDDIES 

These  are  generally  known  in  aviation  parlance  as  "bumps."  Obstacles  in  the  path 
of  moving  air  at  the  surface  cause  them.  They  are  strongest  on  the  leeward  side  of 
hills,  buildings,  or  other  elevations,  and  most  noticeable  in  a  strong  wind.  Figure  111 
illustrates  the  action  of  the  air.  If  landing  is  forced,  the  aviator  should  select  the 
windward  side  of  the  obstruction  or  a  point  well  away  to  leeward. 

AERIAL  TORRENTS 

The  aerial  torrent  is  caused  by  air  colder  than  the  surrounding  air  pouring  down- 
ward. Great  velocity  is  attained  on  surface  slopes  or  open  valleys.  The  effect  on  the 
airplane  is  exactly  opposite  that  of  the  aerial  fountain  illustrated  in  Figure  108. 


142 


Practical    Aviation 


Figure  112 — Cirrus  (Afare's  Tails),  alti- 
tude 30,000  feet  or  more.    Predict  wind 
and  cyclonic  depression 


Figure  115 — Nimbus   (rain  cloud),  alti- 
tude 300  to  6,500  feet.     Steady  rain  or 
snow  usually  falls 


Figure      113  —  Alto-Cumulus;     altitude 

10,000   to   23,000   feet.     Indicate   strong 

cross  currents  of  air 


Figure  116 — Cumulus  (woolsack  clouds), 
altitude  4,500  to  6,000  feet.     Cause  vio- 
lent  disturbances  to   the  airplane 


Figure     114 — Strata -Cumulus;     altitude 

6,500    feet.      Large    globular    masses    or 

rolls,    frequently    covering    whole    sky. 

Predict  a  change  in  weather 


Figure    117 — Cumulo-Nimbus    (thunder 
cloud),  altitude  4,000  to  26,000  feet.  Dan- 
gerous   to    aviators    because    of    strong 
currents   and    electric    effects 


Weather  Forecasting  by  Clouds  143 

CLOUDS  AND  THEIR  SIGNIFICANCE 

CLOUDS 

Clouds  are  formed,  (a)  by  condensation  when  an  ascending  mass  of 
moist  air  encounters  another  moist  mass  of  different  temperature;  (b)  by 
cooling,  when  an  ascending  column  of  vapor,  mixed  with  particles  of  dust, 
condenses.  Types  of  clouds  and  their  direction  indicate  the  weather  to  the 
observing  aviator.  Clouds  are  either  in  the  form  of  sheets  or  heaps,  and  may 
be  so  studied. 

CLASSIFICATION  OF  CLOUDS 

Cirrus — (Mare's  Tails.)  Light  wisps  of  whitish  cloud,  of  fibrous  appearance  with 
no  shadows.  These  clouds  are  the  highest  in  the  international  classification,  commonly 
appearing  at  an  altitude  of  30,000  feet  or  more.  They  predict  wind  and  a  cyclonic 
depression.  Illustrated  in  Figure  112. 

Cirro-Stratus — A  thin  sheet  of  tangled  web  structure,  whitish,  and  sometimes 
covering  the  sky  completely,  giving  it  a  milky  appearance.  This  cloud  often  creates  sun 
and  moon  halos.  Its  average  height  is  29,500  feet.  Forecasts  bad  weather. 

Cirro-Cumulus — (Mackerel  Sky.)  Small  globular  masses  or  white  flakes  without 
shadows,  or  showing  very  light  shadows,  arranged  in  groups  and  often  in  lines.  Aver- 
age height  between  10,000  and  23,000  feet.  Denotes  fine  weather. 

Alto-Stratus — A  thick  sheet  of  gray  or  bluish  color,  sometimes  forming  a  compact 
mass  of  dark  gray  color  and  fibrous  structure.  Often  causes  brilliant  coronae  when 
near  sun  or  moon.  Average  height  10,000  to  23,000  feet. 

Alto-Cumulus — Large  globular  masses,  white  or  grayish,  partially  shaded,  arranged 
in  groups  or  lines,  and  often  so  closely  packed  that  their  edges  appear  confused. 
Illustrated  in  Figure  113.  This  cloud  formation  is  somewhat  similar  to  the  mackerel 
sky  (cirro-cumulus) ;  it  has  the  same  elevation,  10,000  to  23,000  feet.  The  cross  lines 
indicate  strong  cross  currents  of  air. 

Strato-Cumulus — Large  globular  masses  or  rolls  of  dark  clouds,  frequently  covering 
the  whole  sky,  especially  in  winter.  Altitude  6,500  feet.  Illustrated  in  Figure  114. 
Predict  a  change  in  weather. 

Nimbus — A  thick  layer  of  dark  clouds  without  shape  and  with  ragged  edges  from 
which  steady  rain  or  snow  usually  falls.  Shown  in  Figure  115.  Through  the  openings 
an  upper  layer  of  cirro-stratus  or  alto-stratus  is  almost  invariably  seen.  Low  elevation, 
300  to  6,500  feet. 

Cumulus — (Woolpack  Clouds.)  Thick  clouds  of  which  the  upper  surfaces  are 
dome-shaped  with  protuberances;  base  horizontal.  Illustrated  in  Figure  116.  They  indi- 
cate the  aerial  fountain  and  are  low  flying,  4,500  to  6,000  feet.  Violent  disturbances  to 
the  airplane  will  be  experienced  when  passing  through  them,  or  passing  above  or  below. 

Cumulo-Nimbus — (Thunder  Cloud.)  Heavy  masses  of  cloud  rising  in  the  form,  of 
mountains  or  turrets  or  anvils,  generally  surmounted  by  a  sheet  or  screen  of  fibrous  ap- 
pearance (false  cirrus)  and  having-  at  its  base  a  mass  similar  to  nimbus  (rain  cloud). 
Illustrated  in  Figure  117.  Apex  10,000  to  26,000  feet;  base,  4,000  feet.  Dangerous  to 
aviators,  because  of  strong  currents  and  electric  effects. 

Stratus — A  uniform  layer  of  cloud  which  resembles  fog  but  does  not  rest  on  the 
ground.  It  usually  is  stationary  or  drifting  slowly  at  altitudes  of  100  feet  to  3,500  feet. 

GENERAL  OBSERVATION 

Aviators  may  gain  valuable  knowledge  of  existing  wind  currents  by 
observation  of  clouds.  The  general  rule  is  that  unbroken  clouds  indicate 
smooth,  even  air  flow,  broken  formations  the  presence  of  air  currents.  The 
behavior  of  these  currents  may  be  anticipated  by  applying  the  above  class- 
ification to  the  clouds  in  evidence. 


144 


Practical    Aviation 


good  illustration  of  how  an  airplane  may  drop  to  dangerous  levels  when  coming  out  of  an 

aerial  fountain 


Practical    Aviation  145 


REVIEW  QUIZ 

Meteorology  for  the  Airman 

1.  In  what  way  is  ability  to  apply  the  laws  of  weather  forecasting  a 

safeguard  for  the  aviator? 

2.  Why  are  calm,  clear  days  best  for  flying? 

3.  From  which  direction  do  winds  carrying  least  "bumps"  blow  in  the 

United  States? 

4.  State  the  percentage  of  air  weight  below  3  miles  altitude. 

5.  Define  atmospheric  pressure. 

6.  Describe  the  processes  by  which  air  at  rest  is  given  motion. 

7.  What  instrument  measures  air  pressure? 

8.  How  are  pressure  areas  indicated  on  weather  maps,  and  how  can 

the  aviator  secure  valuable  cross-country  flight  data  from  these 
indications? 

9.  State  the  difference  between  high  and  low  pressure  areas  and  give 

another  meteorological  term  to  describe  them. 

10.  What  weather  is  indicated  by  wedges? 

11.  Explain  why  line   squalls  are   dangerous  to   airmen  and  give   the 

barometer  indications. 

12.  State  the  velocity  increase  and  veering  of  wind  at  1,000,  2,000  and 

3,000  feet. 

13.  Define  an  aerial  fountain  and   its  action  on  an  airplane   entering, 

leaving  and  grazing  it. 

14.  Why  should  aviators  avoid  landing  in  aerial  cataracts? 

15.  Explain  the  action  of  a  vertical  wind  eddy  and  how  a  landing  in 

such  should  be  made. 

16.  Give  two  convenient  classifications  of  cloud  forms. 

17.  Name  and  describe  a  type  of  cloud  which  predicts  bad  weather. 

18.  Give  the  name  and  appearance  of  a  type  of  cloud  which  denotes 

fine  weather. 

19.  Name  :and  define  four  cloud  formations  which  indicate  winds  un- 

favorable to  flying. 

20.  State  a  general  rule  for  distinguishing  smooth  air  from  that  with 

cross  currents  by  observation  of  the  clouds. 


146 


Practical    Aviation 


CHAPTER  ANALYSIS 

Aerial  Gunnery  and  Combat 
Bombs  and  Bombing 


COMBAT  AIRPLANES: 

(a)  Function. 

(b)  Employment. 

FACTORS  OF  SUCCESS  IN 
AIR  COMBAT: 

(a)  Airplane  Superiority. 

(b)  Strategy. 

(c)  Aerial   Gunnery. 

THE  LEWIS  MACHINE  GUN: 

(a)  General  Description. 

(b)  Operating  the  Gun. 

(c)  Loading. 

(d)  Firing. 

ACCURACY  AND  VOLUME 
OF  FIRE: 

(a)  Accuracy. 

(b)  Volume. 

(c)  Firing  at  Ground  Targets. 

AMMUNITION  AND  FIRE 
CORRECTION : 

(a)  Types  of  Bullets. 

(b)  Correction  of  Fire. 

GUN  MOUNTINGS  AND 
FIRE  RADIUS : 

(a)  Forward  Gun  Mountings. 

(b)  Effective  Angles  of  Fire. 

FIGHTING  IN  THE  AIR: 

(a)  Skill   in  Attack. 

(b)  Methods  of  Attack. 


AERIAL   TACTICS: 

(a)  Flying  in   Formation. 

(b)  The    Start. 

(c)  The   Flight. 

(d)  Signals   in   Formation. 

(e)  Employment  of  the  Air  Fleet. 

(f)  Theory   of   Concentration. 

(g)  Warfare  Altitudes, 
(h)  Tactical  Skill. 

CONTACT  PATROL: 

(a)  Scope  of  the  Observation. 

(b)  Trench  Offensives. 

ANTI-AIRCRAFT    FIRE: 

(a)  Action  Under  Fire. 

(b)  Location  and  Types  of  Guns. 

(c)  Shell  Trajectories  and  Ballis- 

tics. 

(d)  Defending   Positions. 

(e)  Attacks  on  Balloons. 

BOMBING  AIR  RAIDS: 

(a)  Types  of  Bombing  Airplanes. 

(b)  Mufflers  and   Flares. 

(c)  Training    Bombing   Crews. 

TYPES   OF  BOMBS: 

(a)  Incendiary    Bombs. 

(b)  Safety  Devices. 

(c)  Explosive   Bombs. 

(d)  Bomb   Carriers   and    Launch- 

ing  Cradles. 

(e)  Steel  Darts. 

BOMB  DROPPING: 

(a)  Range    Finders. 

(b)  Operation      of      the      Range 

Finder. 


CHAPTER    XIV 

Aerial  Gunnery  and  Combat — Bombs  and  Bombing 

Combat  airplanes,  known  variously  as  pursuit,  chaser  and  fighting  planes, 
have  as  their  main  duty  the  securing  of  superiority  over  the  enemy  in  the 
air,  or  mastery  of  the  air.  Clearing  the  skies  of  hostile  airplanes  over  the 
theatre  of  operations  requires  domination  of  the  air  situation,  repulsing  all 
efforts  of  the  enemy  to  make  observations  of  troop  movements  or  occupied 
positions,  frustrating  all  bombing  raids  or  other  air  offensives,  and  insuring 
the  success  of  these  missions  over  enemy  territory. 

The  work  roughly  divides  itself  into*:    (a)  patrolling,  (b)  sentinel  duty. 

Patrols  comprise  those  for  interior  and  exterior  duty. 

Driving  the  enemy  out  of  the  air  in  a  given  sector  is  accomplished  by 
the  fast  machines  of  the  air  squadron,  speedy  pursuit  planes  taking  the  air 
singly  or  in  small  bodies  and  following  the  hostile  airplanes  to  the  distance 
dictated  by  the  strategic  situation  and  the  co-ordination  with  supporting  air- 
craft. Patrols  are  continuous  when  weather  permits,  and  the  aviators  se- 
lected for  this  duty  are  the  pick  of  the  service,  all  being  skilled  in  air  acrobacy 
which  is  extensively  employed  in  aggressive  and  defensive  fighting.  These 
fighters  seek  combat  at  every  opportunity,  often  cruising  about  singly  or  in 
formation  in  a  roving  search  for  hostile  fliers.  At  other  times  a  definite 
mission  is  determined  in  advance,  perhaps  to  engage  enemy  airplanes  which 
have  been  observed,  or  to  seek  certain  areas  over  which  hostile  air  forces 
are  expected.  Again,  the  objective  may  be  the  destruction  of  enemy  captive' 
observation  balloons,  a  particularly  dangerous  duty  owing  to  the  protection 
afforded  these  by  battleplanes  and  anti-aircraft  batteries. 

Maintenance  of  an  aircraft  screen  is  the  essential  of  sentinel  duty.  Aside 
from  special  missions,  the  fast  combat  planes  are  assigned  to  definite  air 
lanes  or  areas  5,000  to  7,000  feet  above  the  reconnaissance  and  fire  control 
airplanes,  the  fighters  supplying  protection  to  the  slower  observing  craft 
operating  at  2,500  to  3,000  foot  altitudes.  Beating  off  hostile  air  attacks 
is  accomplished  according  to  the  requirements  of  the  situation,  supporting 
combat  craft  closing  in  at  the  point  of  attack.  Pursuit  of  enemy  airplanes 
requires  an  extension  of  patrol  lanes  by  the  machines  remaining  behind,  for 
at  no  time  must  the  observers  be  left  unprotected. 

Combat  planes  are  well  armed  and  placed  in  the  hands  of  the  most 
skilled  and  quick-witted  aviators.  Their's  is  a  great  responsibility,  for  they 
not  only  afford  the  observing  planes  protection  over  the  enemy  lines,  but 
ward  off  attacks  on  friendly  observation  balloons  four  or  five  miles  back 
within  their  own  lines  and  also  accompany  daylight  bombing  missions  to 
engage  attacking  planes. 

Contact  patrol,  or  co-operation  at  low  altitudes  with  infantry  in  assault, 
is  still  another  function,  for  which  great  skill  is  demanded.  Expertness  in 
use  of  the  machine  gun,  thorough  familiarity  with  acrobatics  and  dauntless 
courage  are  the  requisites  of  the  aviator  given  a  combat  plane. 

147 


148 


Practical   Aviation 


Value  of  Technical  and  Strategical  Superiority.  149 

FACTORS  OF  SUCCESS  IN  AIR  COMBAT 

Success  in  airplane  fighting  is  not  a  matter  of  luck  or  due  to  the  un- 
reasoning type  of  dare-devil  assault.  Cool  calculation  and  application  of 
carefully  defined  principles  of  strategy  and  tactics  is  responsible  for  prac- 
tically all  victories. 

The  personal  equation,  always  a  great  factor  in  success  with  arms,  looms  large 
in  air  combat.  Aggressiveness  must  be  combined  with  agility  of  mind  and  technical 
skill  is  of  the  utmost  importance. 

A  third  advantage  rests  with  superiority  in  equipment,  notably  the  speed,  climbing 
and  maneuvering  ability  of  the  airplane,  its  armor  and  the  number  and  type  of  guns 
comprising  its  armament. 

AIRPLANE  SUPERIORITY 

Engaged  singly  in  combat,  it  is  obvious  that  the  advantage  lies  with  the  airplane 
which  has  the  greatest  mobility  of  movement,  being  enabled  by  superior  speed,  climb 
and  flexibility  to  out-maneuver  its  opponent.  The  air-worthiness,  or  flying  qualities, 
determine  which  machine  will  emerge  from  circling  and  diving  to  the  most  favorable 
position,  either  above,  below,  in  rear  or  advance  of  the  enemy  craft,  advantages  de- 
termined by  tactical  considerations  such  as  type,  armament,  number  and  disposition 
of  the  hostile  craft.  Choice  of  position  is  largely  governed  by  the  type  of  airplane. 

Tractors  are  ordinarily  armed  with  two  machine  guns,  operated  either  by  the  pilot 
or  gunner,  or  both.  With  the  pilot  in  the  front  seat,  the  gunner  has  a  wide  arc  of  fire 
to  the  rear,  but  with  the  pilot  in  the  rear  the  gunner  is  in  full  observation  and  the 
machine  is  best  maneuvered  for  direction  of  fire.  Mounting  the  machine  gun  on  the 
top  plane  permits  operation  from  the  rear  seat;  it  therefore  has  obvious  advantages. 
As  combat  airplanes  are  essentially  of,. the  pursuit  type,  the  most  effective  fire  should 
be  to  the  front. 

Pusher  types  are  generally  at  a  disadvantage  because  of  inferior  speed.  But  with 
the  gunner  placed  well  forward  in  the  nacelle  a  wide  arc  of  lateral  and  vertical  fire  is 
obtained.  For  heavier  armament  the  pusher  type  has  undoubted  superiority,  but  in 
firing  backward  through  the  propeller  efficiency  is  lost.  Exception  must  be  made  in 
the  double  propeller  pusher  types  where  the  arc  of  fire  is  clear,  but  although  both 
tractor  and  pusher  have  separate  advantages  and  both  have  many  advocates,  the  speed 
and  mobility  of  the  tractor  type  give  it  a  definite  point  of  superiority. 

STRATEGY 

Familiarity  with  the  appearance  of  various  types  of  enemy  airplanes,  which  is 
essential  knowledge  to  the  military  aviator,  includes  an  estimate  of  their  speed  and 
mobility,  number,  disposition  and  range  of  guns,  and  the  best  means  of  attacking  in 
each  case. 

The  former  "blind  spot,"  i.e.,  under  the  tail,  is  now  defended  by  a  machine  gun 
which  shoots  through  a  tunnel  in  the  fuselage;  thus  the  approach  from  the  rear,  firing 
upward,  is  no  longer  a  fundamental  principle  of  attack.  Clouds  and  the  sun  may  be 
usefully  employed;  for  to  get  between  the  enemy  and  the  sun  blurs  the  outline  of  the 
approaching  plane.  Hiding  behind  clouds  and  diving  carries  the  element  of  surprise 
and  is  widely  employed. 

Acrobacy  is  an  essential  accomplishment,  for  a  general  rule  governing  air  combat, 
in  event  of  failure  in  surprise  attack,  is  to  duplicate  every  movement  of  the  enemy 
engaged.  If  a  diving  attack  is  made  the  adversary  dives,  looping  or  zooming  before 
the  hostile  machine  guns  are  within  range,  thus  reversing  the  position  and  gaining  the 
altitude  advantage.  The  same  is  true  of  climbing;  the  pursuer  also  climbs,  attempting 
by  superior  climbing  ability  to  reach  a  position  where  he  can  dive  at  his  opponent. 
Short  rises  and  dives  in  quick  succession  constitute  an  effective  form  of  attack  on  a 
machine  armed  with  two  or  more  guns.  Direct  hits  by  machine  gun  fire  are  difficult 
of  accomplishment  and,  due  to  the  frequent  misses,  air  combat  remains  largely  a 
matter  of  skilful  acrobacy.  The  operation  of  the  airplane  must  be  instinctive  with  the 
fighting  aviator,  aerial  evolutions  being  accomplished  without  a  second  thought,  so  the 
greater  concentration  may  be  given  to  accuracy  of  fire. 

Jamming  of  machine  guns  is  frequent,  often  occurring  at  the  crucial  moment,  and 
temporarily  disarming  the  fighting  pilot;  a  quick  escape  is  then  required.  This  can 
seldom  be  effected  by  straight-away  flight  at  high  speed  toward  friendly  territory, 
owing  to  the  target  the  machine  will  thus  present.  Side  slips  and  spins,  in  fact  all 
forms  of  aerobatics  which  give  the  appearance  of  an  airplane  falling  out  of  control,  are 
resorted  to,  the  machine  being  straightened  out  when  well  out  of  range.  At  all  times, 
therefore,  the  fighting  aviator  must  know  his  position  in  reference  to  his  own  lines, 
for  aerial  combat  may  take  him  many  miles  within  enemy  territory.  An  aviator  is 
ordered  to  take  no  chances  when  odds  are  against  him,  and  strategy  demands  that  an 
escape  be  attempted  if  anything  goes  wrong  with  his  machine  or  gun. 


150 


Practical    Aviation 


Description  and  Operation  of  Machine  Gun  151 

THE  LEWIS  MACHINE  ,GUN 

This  weapon  is  a  standard  airplane  arm,  weighing  about  16  pounds, 
simple  in  action  and  with  comparatively  few  parts.  Success  in  its  handling* 
is  largely  dependent  upon  the  operator's  familiarity  with  the  piece.  The 
fighting  aviator  should  have  full  knowledge  of  all  parts  of  the  gun  and  be 
able  to  dismount,  assemble  and  adjust  it  without  stopping  to  think  about 
the  process.  To  recognize,  instantly,  any  fault  in  its  operation  while  firing 
and  to  correct  it  without  hesitation  is,  broadly  speaking,  the  skill  required. 

GENERAL  DESCRIPTION 

The  Lewis  machine  gun  is  air-cooled  gas  operated,  and  magazine-fed. 
The  magazine  is  a  circular  drum  in  which  the  cartridges  are  arranged  radially ; 
the  bullet  ends  are  toward  the  center  and  are  engaged  by  a  spiral  groove 
in  the  magazine  center,  down  which  the  cartridges  are  driven  until  they 
are  successively  reached  by  the  feed  operating  arm.  While  firing  the  other 
parts  of  the  magazine  are  rotated  about  the  center.  Gas  pressure,  produced 
in  the  barrel  by  the  exploding  cartridge,  furnishes  the  motive  power  for 
operating  the  mechanism.  This  gas,  drawn  into  a  cylinder  through  a  hole 
near  the  muzzle  of  the  barrel,  drives  a  piston  back,  and  thus  winds  the  main- 
spring which  operates  the  breach  bolt  and  ejector,  feeds  a  new  cartridge, 
and  rotates  and  locks  the  magazine.  If  the  trigger  is  held  back  the  firing 
is  continuous  until  the  magazine  holding  100  cartridges  has  been  emptied. 
To  fire  a  single  shot  the  trigger  is  pressed  and  released  immediately. 
OPERATING  THE  GUN 

By  constant  reference  to  the  drawing  of  the  Lewis  gun  in  section,  Figure  118,  the 
reader  will  understand  its  operation  in  detail  from  the  following  description: 

Loading — The  charging  handle  (see  slot  at  rear  of  8-1  Rack  on  drawing)  is  placed 
in  full  forward  position,  the  magazine  placed  on  its  post  and  pressed  down,  thumb 
piece  of  magazine  latch  to  right.  The  charging  handle  is  then  drawn  back  fully  until 
it  is  engaged  and  held.  This  draws  back  the  piston,  drawing  the  rack  teeth  over  the 
teeth  of  the  gear  (9-7)  which  rotates  the  gear  and  winds  its  mainspring.  During  the 
rearward  travel,  the  striker  (8-2)  has  been  drawn  back  from  the  face  of  the  bolt  and 
the  bolt  rotated  from  right  to  left,  turning  the  locking  lugs  out  of  their  recesses.  As 
the  bolt  is  unlocked  the  striker  post  carries  it  back  with  it.  The  feed  operating  arm 
is  swung  across  the  top  of  the  receiver  by  the  feed  operating  stud  (4-1);  and  the  feed 
pawl  (7-2),  acting  against  one  of  the  outer  projections  of  the  magazine  pan,  carries 
the  magazine  around  sufficiently  to  drive  the  first  cartridge  down  the  spirally  grooved 
center  into  the  opening  in  the  feed  operating  arm.  This  is  the  position  pictured  in 
the  drawing,  Figure  118.  The  feed  operating  arm  brings  the  cartridge  under  control 
of  the  cartridge  guide  and  a  spring  stud  clears  the  stop  pawl,  which  presses  forward 
and  prevents  further  rotation  of  the  magazine.  Meanwhile  the  rear  end  of  the  bolt 
has  driven  the  ejector  into  its  slot,  and  the  rear  end  of  the  piston  rack  has  set  the  sear 
spring  which  cocks  the  piece. 

Firing — When  the  trigger  is  pressed,  the  sear  is  drawn  out  of  engagement  with 
the  notch  in  the  rack,  the  latter  being  then  drawn  forward  by  the  unwinding  of  the 
mainspring,  rotating  the  gear  in  mesh  with  the  rack. 

In  the  forward  motion  of  the  bolt  a  stud  cams  the  feed  operating  arm  to  the  right, 
a  spring  stud  on  the  latter  pressing  the  stop  pawl  back  from  the  magazine  projection; 
the  head  of  the  bolt  now  presses  the  ejector  into  'its  cut  and  the  face  of  the  bolt, 
striking  the  base  of  the  waiting  cartridge,  takes  it  from  the  loading  ramps  of  the 
receiver  and  drives  the  cartridge  into  the  chamber.  The  extractors  spring  over  the 
rim  as  the  cartridge  seats.  The  bolt  locking  is  completed  by  the  forward  motion  ot 
the  striker  post,  which  then  enters  the  front  part  of  its  cut,  carrying  the  striker  against 
the  cartridge  primer  and  firing  it. 

The  firing  of  the  cartridge  develops  the  power  for  another  cycle  of  operation.  As 
the  gas  which  drives  the  bullet  forward  reaches  near  the  muzzle  of  the  barrel  it  is 
driven  down  through  a  hole  into  the  gas  chamber  (J-34).  Thence  it  ^passes  under 
pressure  through  a  hole,  striking  against  the  head  orthe  piston  and  driving  it  back. 
This  backward  movement  produces  the  movements  of  loading  as  described  above. 
The  empty  shell,  however,  in  the  grip  of  the  extractors  is  drawn  back  with  the  bolt, 
throwing  the  shell  out  of  the  ejector  port. 

If  the  trigger  is  held  back  the  gun  will  fire  again  and  continue  the  cycle  of  opera- 
tions at  the  rate  of  about  10  shots  per  second  until  the  magazine  is  empty. 


152 


Practical    Aviation 


Figure   119 — The  ditch  target; 
a  splash  records  a  hit 


Figure  120 — The  moving  target  for  ground  practice, 
showing  the  armor  shield  for  the  operator 

ACCURACY  AND  VOLUME  OF  FIRE 

Engagements  between  airplanes  in  combat  are  brief;  thorough  training 
in  aiming  and  delivering  machine  gun  fire  is  therefore  given  a  prominent 
place  in  instructing  the  aviator.  Gunnery  skill  is  the  deciding  factor  between 
opponents  with  equal  technical  advantages  and  flying  ability,  and  at  all  times 
has  considerable  bearing  upon  victory  or  defeat. 
ACCURACY  OF  FIRE 

Due  to  aiming  at  a  constantly  moving  target  from  a  generally  unstable  base,  ac- 
curacy in  fire  is  seldom,  reduced  to  exactness.     Distinct  superiority  in  aiming  may  be 
acquired,  however,  by  diligent  practice  on  simulated  moving  airplanes,  and  is  worth 
all  the  effort  which  may  be  given  it. 
VOLUME  OF  FIRE 

High  rate  of  fire  is  essential  to  an  airplane  arm,  since  the  range  is  of  limited 
length  and  the  duration  of  effective  fire  reduced  to  a  few  seconds.     The  machine  gun 
which  operates  at  greatest  rapidity  and  with   smoothest  action  gives   a   decided  ad- 
vantage, owing  to  the  limitations  in  accuracy  of  aiming. 
FIRING  AT  GROUND  TARGETS 

Two  types  of  targets  are  illustrated  in  Figures  119  and  120.  In  Figure  119  a  circle 
of  sand  is  shown  with  two  intersecting  ditches  in  the  form  and  size  of  an  airplane, 
filled  with  water  so  a  splash  registers  a  hit.  An  observer  under  cover  watches  and 
records  the  number  of  tim.es  the  target  is  struck.  The  airplane  illustrated  has  the 
gun  mounted  rigidly  on  the  upper  plane  and  the  entire  machine  is  aimed  at  the  mark. 
A  flexible  cable  connects  the  gun  trigger  to  a  lever  on  the  control  stick,  the  gun  firing 
as  the  lever  is  squeezed.  An  open  sight  on  a  level  with  the  pilot's  eyes  is  used  for 
aiming. 

An  advanced  instruction  device  on  the  same  principle  utilizes  a  cross  which  re- 
volves on  a  bar,  describing  a  40-foot  circle.  It  is  operated  from  a  protected  trench 
by  means  of  a  cable  and  pulley  which  rotates  the  target  at  the  approximate  speed  of 
an  airplane  in  a  spiral.  The  shots  are  made  at  a  height  of  about  800  feet  above  the 
ground. 

Figure  120  clearly  illustrates  another  form  of  moving  target,  the  truck  being 
operated  by  the  man  seated  behind  the  armored  shield.  Students  fire  at  the  moving 
outlines  of  the  airplane  from  the  ground,  either  from  a  stationary  seat  or  from  the 
pivoted  chassis  shown  in  the  photograph  below,  a  representation  of  an  airplane  cock- 
pit which  sways  at  the  slightest  movement. 


Bullet     Types  and  Fire  Correction 


153 


Ordinary       Perforating  Tracing 


Explosive  expanding 


I 


Figure  121 — Types  of  bullets  used         Figure  122 — No  correction  laterally 

in  airplane  machine  guns  for  de-         Figure  123 — Lateral  correction  for  velocity 

slruction  and  for  correction  of  aim          Figure  124 — Longitudinal  correction  for  velocity 

AMMUNITION  AND  FIRE  CORRECTION 

Correction  of  machine  gun  fire  is  commonly  made  by  observation  of  the  path  of 
phosphorous  tracer  bullets,  placed  about  every  fifth  position  in  the  magazine.  The 
gun  is  deflected,  raised,  or  aimed  to  either  side,  in  accordance  with  the  direction  of 
the  smoke  trail  toward  the  enemy  airplane.  The  objective  is  usually  the  back  of  the 
pilot,  aiming  being  governed  by  its  appearance  in  the  center  of  the  sight.  Various 
types  of  bullets  are  used  in  machine  guns  and  an  understanding  of  their  functions  and 
construction  is  useful. 

TYPES    OF    AMMUNITION 

The  five  common  types  of  bullets  for  air  warfare  are  illustrated  in  section  in  Figure   121. 

ORDINARY — The  head  of  this  bullet  is  usually  of  solid  brass  and  presents  no  new  features. 

PERFORATING — This  type  of  bullet  is  designed  to  pierce  metal,  being  used  against  airplane  motors 
and  fuel  tanks.  The  core  is  ordinarily  of  hard  steel  encased  in  a  covering  of  copper,  zinc  and  nickel  alloy. 

TRACING — These  bullets  are  hollow  and  filled  with  a  phosphorous  compound;  the  casing  is,  an 
alloy  of  copper,  zinc  and  nickel.  They  leave  a  luminous  or  smoke  trail  behind  and  are  combustible ;  they 
are  designed  both  for  fire  correction  and  for  incendiary  purposes. 

EXPLOSIVE — The  bullets  are  made  somewhat  in  the  form  of  a  small  shell;  they  are  hollow  and 
contain  an  explosive  charge  in  the  nose,  consisting  of  chlorate  of  potash  and  sulphur,  in  equal  parts,  acting 
both  as  detonator  and  exploder.  The  lighter,  flattened  nose  gives  this  type  of  bullets  a  different  trajectory 
from  those  of  ordinary  form. 

EXPANDING — Destruction  of  struts  and  spars  is  the  mission  of  the  expanding  type,  drilled  at  the 
nose  so  instantaneous  disintegration  takes  place  even  when  encountering  small  diametered  parts  of  low 

CORRECTION  OF  FIRE 

While  several  formulae  have  appeared  to  determine  accuracy  of  aiming  at  hostile 
machines,  practical  application  is  well  nigh  impossible  because  they  presuppose  a 
knowledge  of  (a)  speed  of  both  airplanes,  (b)  aiming  angle  with  reference  to  flight 
path,  (c)  enemy  machine's  flight  path.  The  hopelessness  of  determining  these  is 
immediately  apparent  without  proper  instruments;  dependence  is  therefore  placed 
upon  the  trail  of  the  tracer  bullet,  although  special  apparatus  for  sighting  which  makes 
an  automatic  correction  has  been  developed,  but  must  not  be  described  just  now. 

A  few  principles  of  sighting  upon  which  correction  calculations  are  based  are  illus- 
trated in  the  diagrams,  Figures  122,  123  and  124.  The  only  correction  necessary  in  the 
case  of  Figure  122  is  a  raising  or  deflection  of  the  gun  or  the  airplane  A,  according  to 
whether  gun  is  fixed  or  movable. 

In  Figure  123,  enemy  airplane  B  has  a  course  at  a  wide  angle  to  the  path  of  A.  Since 
the  enemy  machine  is  moving  forward  at  high  velocity,  it  is  necessary  to  aim  on  the  line 
A,  C,  the  measure  of  correction  being  the  line  B,  C. 

Figure  124  illustrates  the  principle  which  depends  upon  the  angle  of  the  gun  with 
reference  to  the  flight  path,  it  being  necessary  in  this  case  to  make  allowance  for  the  for- 
ward motion  of  both  machines,  aiming  at  an  approximate  point  C}  instead  of  directly  at 
at  enemy  airplane  B. 


154 


Practical    Aviation 


Figures  I25a — Gun  fixed  on  upper  plane  Figure  l2Sb — Firing  through  propeller 


Figure  I26a — Lateral  arc  of  single  movable        Figure    \26b — Longitudinal   arc    of   single 
forward   gun    on  pusher   airplane  movable  forward  gun  on  pusher  airplane 


Figure   127a — Effective   lateral  arc  of 
rear  gun 


Figure  \27b — Effective  longitudinal  arc  of 
rear  gun 


Figure   128a — Arcs  of  forward  fixed  and         Figure  I28b — Longitudinal  arc  of  fire  with 
movable  rear  gun  same  arrangement 


\ 


T 


,""]  r> 


Figure  129a — Joining  arcs  of  two  mobile  guns      Figure  I29b — Longitudinal  radius  of  action 


Values  of  Various  Gun  Arrangements  155 

GUN  MOUNTINGS  AND  FIRE  RADIUS 

Placing  of  machine  guns  and  their  number  on  enemy  airplanes  is  a  matter  for 
exact  knowledge  with  the  military  aviator.  From  recognition  of  a  type  he  can  estimate 
his  chances  of  evading  its  fire  and  the  best  points  of  attack. 

The  various  arrangements  of  armament  of  hostile  airplanes  becomes  thoroughly 
familiar  in  sectors  where  daily  engagements  are  the  rule,  and  although  distribution 
and  number  of  machine  guns  are  subject  to  constant  change,  acquaintance  with  the 
field  of  fire  and  mobility  of  the  various  arms  establish  certain  principles  which  arc 
fundamental  and  determine  the  possibilities  of  all  modifications.  Account  must  be 
taken  of  the  value  of  surprise  in  arranging  armament.  A  brief  discussion  of  the  effec- 
tive fire  secured  by  the  various  arrangements  follows: 

FORWARD  GUN  MOUNTINGS 

The  first  consideration  in  placing  forward  guns  in  tractor  types  is  their  location. 
Figure  125-a  illustrates  the  machine  gun  fixed  to  the  upper  plane  and  firing  over  the 
propeller;  Figure  125-b  gives  the  arrangement  for  firing  through  the  propeller,  as 
usually  placed  in  one-man  airplanes.  Placing  the  gun  on  the  top  plane  has  two  disad- 
vantages: Resistance  to  the  air,  increasing  the  drift  and  consequently  lessening  lift, 
and  difficulty  in  reloading  the  gun.  To  remove  the  empty  magazine  and  replace  it 
with  a  loaded  one  requires  turning  the  gun  upside  down.  When  it  is  considered  that 
the  rate  of  fire  is  so  rapid  that  the  magazine  is  emptied  in  10  or  15  seconds,  it  is 
obvious  that  unless  a  hit  is  made  with  the  emptying  of  the  first  magazine  the  airplane 
is  helpless  in  the  matter  of  further  immediate  attack. 

Shooting  through  the  propeller  is  accomplished  by  synchronizing  the  discharge 
of  the  gun  with  the  revolutions  of  the  propeller,  the  mechanism  being  governed  by 
the  motor.  The  device  is  timed  to  suspend  discharge  when  the  blades  are  passing  thi 
muzzle  of  the  gun;  thus  with  a  propeller  revolving  at  the  rate  of  1400  r.p.m.  the  two 
blades  pass  that  point  at  intervals  of  1-47  of  a  second,  a  fraction  of  time  which  has 
no  material  bearing  upon  maintenance  of  virtually  continuous  fire. 

Armoring  the  propeller  blades  to  deflect  the  bullets  is  another  method  which  has  been  employed,  but 
is  not  favored  to  as  great  an  extent  as  synchronizing.  Triangular  pieces  of  hard  steel  set  in  the  blades 
at  the  point  of  the  bullets'  path  save  the  propeller  from  breaking,  under  this  method,  and  deflect  the  bullets 
striking  them,  the  percentage  of  loss  being  negligible,  as  low  as  5  to  8  per  cent.  Tapering  the  propeller  at 
the  point  of  the  steel  plate  inset,  however,  means  a  loss  in  tractive  efficiency,  lessening  airplane  speed 
as  much  as  12  miles  per  hour,  a  consideration  of  so  great  importance  as  to  make  the  method  inferior  to 
the  synchronizing  application. 

EFFECTIVE  ANGLES  OF  FIRE 

The  various  arrangements  of  machine  guns  pictured  on  page  154  are  worthy  o:r 
careful  study  by  the  military  aviator. 

Figures  126-a  and  126-b  show  the  application  of  a  single  forward  gun  to  an  airplane 
of  pusher  type,  the  weapon  being  pivoted  in  the  front  of  the  nacelle.  The  dotted 
lines  show  the  limitations  of  the  lateral  and  longitudinal  arcs  of  effective  fire,  and  the 
shaded  portions  the  considerable  dead  area  behind,  the  sides  and  rear  being  particular 
points  of  vulnerability. 

Figures  127-a  and  127-b  illustrate  the  placing  of  a  gun  in  the  cockpit  of  a  tractor 
machine,  giving  it  a  wider  arc  of  effective  fire  to  the  sides  and  above  and  below,  but 
still  leaving  considerable  dead  area  in  front.  The  fact  that  this  blind,  or  undefended, 
spot  is  in  full  view  of  the  pilot  who  is  maneuvering  the  machine  makes  it  less  vul- 
nerable than  in  the  case  of  Figure  126. 

Figures  128-a  and  128-b  show  the  tractor  airplane  with  the  addition  of  a  forward 
gun  shooting  through  the  propeller.  The  arc  of  fire  of  this  gun  is  governed  by  the 
mobility  of  the  airplane,  that  is,  its  radius  of  effective  action  depends  upon  the  skill 
of  the  pilot  and  the  machine's  maneuvering  ability  in  his  hands,  since  the  gun  is 
pointed  by  the  change  of  direction  in  the  entire  airplane.  A.S  this  gun  is  mainly  for 
offensives,  the  rear  gun's  function  is  principally  defensive,  a  wide  arc  of  fire  to  the  rear 
enabling  it  to  ward  off  attacks  from  many  directions.  This  arrangement  of  guns  is 
generally  found  on  lijrht  bombing  and  reconnaissance  or  fire  control  machines. 

Figures  129-a  and  129-b  illustrate  the  effective  armament  of  either  tractor  or 
pusher  types  having  two  propellers.  These  machines  are  largely  used  for  bombing 
and  protection  of  aircraft  or  military  bases,  the  armament  being  of  great  defensive 
value.  Airplanes  of  this  class  with  tractor  screws  are  armed  with  the  additional  gun 
shooting  through  a  tunnel  under  the  fuselage  already  referred  to.  In  type  of  machine 
many  modifications  appear,  but  this  form  of  armament  is  general  with  practically 
all  airplanes  carrying  three  or  more  men. 


156 


Practical    Aviation 


Figure  130 — How  a  supporting  airplane  remains  hidden  from  an  attacking  enemy 


Figure   131 — A   formation  engaging   a  single   enemy,   the   leader  taking   higher 
altitude  for  surprise  attack 


Figure  132 — The  usual  method  of  formation  attack  on  a  single  enemy 


Methods  of  Attack  and  Combat  Rules 


157 


Figure  134 — Employing  the  Immelman  turn  to  effect  an 
escape  from  an  attack  in  formation 


figure     133— The     steep 

angle  for  dive  attack 
FIGHTING  IN  THE  AIR 

Pilots  of  combat  airplanes  must  be  physically  fit  and  mentally  alert  at  all  times. 
The  enemy's  qualifications  for  success  are  fully  as  great,  and  success  is  gained  only  by 
dauntless  courage  governed  by  quick-witted  application  of  flying  and  gunnery  skill. 
The  following  principles  governing  individual  actions  in  combat  are  to  be  observed: 
SKILL  IN  ATTACK 

As  in  all  forms  of  military  science,  surprise  contributes  largely  to  success.  The 
surprise  attack  is  best  delivered  from  a  position  between  the  enemy  craft  and  the  sun. 
Diving  on  the  tail  is  the  favored  method. 

While  diving,  the  rear  should  be  watched;  another  enemy  airplane  may  be  above. 

Except  when  coming  to  the  assistance  of  friendly  aircraft,  speeds  below  100  miles 
per  hour  should  be  employed,  as  excessive  velocities  make  the  airplane  difficult  of 
control  and  the  period  for  machine  gun  fire  too  brief. 

Fire  should  be  withheld  until  within  100  yards  of  the  enemy;  the  glove  on  the 
trigger  hand  is  usually  removed. 

The  machine  on  top  has  the  advantage.  Attack  from  behind  is  most  effective; 
right  angle  fire  is  second  choice,  and  attacking  from  in  front  the  least  effective  method. 

When  the  enemy  airplane  has  superiority  of  speed  the  dive  attack  is  used.  If  the 
hostile  machine  is  inferior,  the  dive  is  made  to  his  rear  to  a  point  a  trifle  below  his 
tail;  before  opening  fire  flying  speed  is  equalized  by  throttling  the  motor. 

Careful  survey  of  the  sky  should  be  made  before  attacking  a  single  enemy  air- 
plane flying  at  a  low  altitude,  as  it  may  be  a  decoy. 

The  tail  is  the  most  vulnerable  spot  of  the  airplane;  attacks  may  be  delivered  and 
expected  most  frequently  at  this  point. 

A  one-man  machine  should  not  return  to  combat  with  a  two-seater  if  the  larger 
enemy  craft  has  the  position  advantage  when  it  opens  fire. 

When  flying  in  formation  superiority  of  numbers  decides  the  advisability  of  attack; 
position  in  formation  lost  in  combat  should  be  regained  at  the  earliest  opportunity. 

METHODS    OF   ATTACK 

Figures  130  to  133  show  some  forms  of  air  tactics  in  combat.  Figure  130  illustrates  a  common 
method  of  support,  airplane  B  remaining  above  clouds  ready  to  assist  airplane  A  which  is  engaged  in 
combat  with  enemy  E,  or  to  attack  any  plane  coming  to  the  assistance  of  E. 

Attack  on  an  airplane  which  has  encountered  a  hostile  formation  is  illustrated  in  Figure  131.  The 
single  enemy  is  surrounded  and  attacked  from  all  sides,  the  leader  of  the  formation  remaining  at  a  higher 
altitude  and  suddenly  diving  on  his  tail  with  a  burst  of  machine  gun  fire. 

The  method  usually  employed  for  attack  on  a  single  enemy  by  three  airplanes  flying  in  formation  is 
shewn  in  Figure  132.  Planes  A  B  and  C  are  discovered  by  enemy  E,  who  immediately  dives  to  escape. 
The  leader  A  opens  the  attac:<  by  diving.  Missing  fire,  he  turns  off  to  the  left  (path  A1-A2).  Airplane 
B,  about  300  feet  behind  at  slightly  higher  altitude,  dives  and  fires;  missing,  he  turns  off  right  at  B2, 
leaving  the  remaining  plane  of  the  formation  C,  in  a  steeper  dive,  to  intercept  the  enemy  at  E3. 

Attempted  escape  from  a  superior  force  by  diving  is  seldom  resorted  to  unless  the  lone  machine  has 
known  superiority  in  diving  speed.  The  usual  method  of  getting  away  is  by  resort  to  air  acrobatics, 
Fieure  134  illustrating  how  the  Immelman  Turn  can  be  successfully  employed  under  the  circumstances. 

Figure  133  demonstrates  the  steeper  diving  angle  required  of  the  attacking  airplane  when  the  adversary 
is  also  diving. 


158  Practical    Aviation 


Figure  135 — An  American  squadron  flying  in   V -formation 
FLYING  IN  FORMATION 

Offensive  combat  in  the  air  is  seldom  sought  by  a  single  airplane,  well- 
defined  and  planned  attacks  against  definite  objectives  generally  being  con- 
ducted by  groups  of  machines,  known  variously  by  the  terms  wings,  squadrons 
and  fleets,  according  to  their  composition  and  numbers.  The  V-formation, 
illustrated  in  Figure  135,  presents  many  advantages  and  is  almost  universally 
employed  for  air  offensives. 

In  this  arrangement  the  leader,  who  has  the  point  and  is  in  command,  may  keep 
all  the  machines  easily  under  observation  and  his  signals  are  seen  without  effort  by  all 
the  pilots.  The  stations  are  determined  in  advance  and  each  pilot  takes  his  assigned 
position  as  close  as  possible  to  the  other  machines  and  slightly  higher  than  the  air- 
plane immediately  ahead.  The  formation  is  copied  from  the  flight  of  birds,  the  aero- 
dynamic reason  for  its  adoption  being  that  the  air  in  the  wake  of  an  airplane  has  a 
downward  motion  unfavorable  to  flight,  whereas  the  vertical  character  of  the  air 
stream  to  both  sides  of  the  leader  has  residuary  upward  motion.  A  military  reason 
for  the  V  preference  over  a  possible  diamond-shaped  arrangement,  is  that  in  the  latter 
three  airplanes  in  the  rear  would  be  open  to  attack  instead  of  two. 
THE  START 

Upon  the  leader  rests  the  responsibility  of  choosing  pilots  and  machines  suitable 
for  flying  in  one  formation.  As  a  general  rule  it  is  important  that  each  aviator  take 
aloft  an  airplane  with  which  he  is  entirely  familiar.  The  machines  and  their  pilots 
are  assembled  some  minutes  before  the  time  set  for  the  start,  their  clothing  and 
equipment  known  to  be  proper  for  the  mission,  pilots  seated  and  all  engines  running 
throttled  down,  before  the  leader  takes  to  the  air. 

Once  the  leader  is  off  the  ground  the  other  airplanes  follow  as  near  as  possible 
in  their  formation  order  at  intervals  of  15  seconds.  Attaining  a  height  of  600  to  800 
feet  in  straight-away  flight,  the  leader  throttles  down  and  watches  the  others  pick  up 
formation.  This  should  be  accomplished  at  a  maximum  rate  of  about  a  half-minute 
per  man.  By  rocking  his  airplane  laterally,  the  leader  then  signals  attention — at 
night  a  red  light  is  fired  from  a  Very  pistol — and  the  climb  is  begun.  If  a  turn  is  re- 
quired to  head  in  the  direction  of  the  objective,  it  is  made  in  advance  of  the  climb  and 
before  the  motor  is  opened  up. 

THE  FLIGHT 

Constant  watchfulness  of  the  progress  of  his  formation  is  required  of  the  leader;  he  verifies  the  posi- 
tion of  each  airplane  by  looking  around  at  intervals  of  one  minute  or  less.  The  speed  of  the  leader  in 
climbing  must  be  adjusted  to  the  slowest  airplane  in  the  formation  or  the  flight  will  be  ragged  from 
the  beginning.  Since  speed  is  of  paramount  importance  in  air  tactics,  not  only  must  the  machines  in 
formation  be  carefully  selected  for  equal  flying  qualities  but  every  pilot  must  hold  his  position  with  greatest 
possible  exactness.  Dropping  out  of  place  tends  to  slow  up  the  progress  of  the  entire  formation  and  loss 
of  position  is  for  each  individual  a  matter  of  grave  importance. 

Turning  is  done  at  a  signal  from  the  leader,  who  rocks  his  airplane  repeatedly  and  pauses ;  he  then 
turns  in  the  desired  direction  in  a  small  arc,  throttling  his  engine  and  nosing  down  a  trifle.  Assume  the 
turn  to  be  to  the  right.  The  airplanes  following  on  the  right  arm  of  the  inverted  V  are  throttled  down 
and  execute  at  slower  speed  a  slight  turn  left,  turning  right  when  the  leader  has  turned ;  meanwhile 
those  on  the  left  have  successively  made  riprht  turns  with  the  motor  on  full.  When  all  have  turned  the 
leader  verifies  the  alignment  and  resumes  full  speed  ahead. 

Lateral  rocking  of  the  airplane  is  the  attention  signal. 

Waving  the  arm  and  the   direction   it  points  indicates  enemy   aircraft. 

The  attention  signal  followed  by  rocking  longitudinally  signifies  a  machine  pvn  .iam. 

While  over  hostile  territory  the  difficulties  of  remaining  in  position  are  increased  by  anti-aircraft  gun- 
fire and  the  formation  is  often  broken;  but  since  success  in  attack  is  largely  governed  by  the  leader's 
freedom  from  concern  about  his  force  holding  together,  all  pilots  should  regain  position  at  the  earliest 
moment.  Constant  vigilance  should  also  be  directed  to  preventing  surprise  attacks  on  the  two  rear  airplanes. 


Tactical  Fundamentals  and  Calculations  159 

EMPLOYMENT  OF  THE  AIR  FLEET 

The  plan  of  action  is  generally  given  to  all  pilots  before  a  formation 
takes  the  air.  Each  man  is  expected  to  know  his  part  in  attainment  of  the 
objective  and  the  leader's  decision  on  the  best  method  of  attacking  a  hostile 
air  force  when  sighted  must  be  transmitted  quickly  by  pre-arranged  signals. 

THEORY  OF  CONCENTRATION 

Superiority  of  numbers  is  the  general  indication  of  the  probability  of  success, 
although  estimate  of  speed  and  armament  of  the  enemy  must  be  taken  into  account, 
along  with  the  altitude  advantage.  Despite  the  growing  tendency  to  the  use  of  armor 
protection,  mobility  of  action  is  thereby  reduced  and  the  upper  position  still  remains 
a  great  tactical  advantage.  Lanchester,  of  the  British  Advisory  Committee  for  Aero- 
nautics, has  evolved  what  he  terms  the  N-Square  Law,  by  which  calculations  on  the 
probable  chance  of  success  may  be  reduced  to  mathematics.  Application  of  the 
N-Square  Law  assumes  equality  in  technical  equipment,  gunnery  and  individual  air- 
manship, the  fighting  strength  of  opposing  forces  being  then  proportionate  to  the 
square  of  numerical  strength  multiplied  by  the  fighting  value  of  individual  units.  Two 
forces  may  be  thus  represented: 

Enemy— 10  airplanes,  or  102       100 

Friendly  =   8  airplanes,  or     82         64 

Enemy's  superiority        36 

The  importance  of  superior  tactics  against  the  enemy  is  then  shown  by  the  as- 
sumption that  the  hostile  formation  is  broken  up,  divided  in  half  and  attacked 
separately.  The  fighting  value  then  appears: 

Friendly  =   8  airplanes,  or  82  64 

Enemy  — 10  airplanes,  or  52-f-52     50 

Friendly  force's  superiority     14 

While  application  of  the  N-Square  Law  may  only  reflect  the  probability  of  success 
in  a  theoretical  way,  similar  mathematical  calculations,  its  creator  points  out,  have  been 
used  deliberately  or  unconsciously  by  great  military  leaders  of  the  past. 

While  superiority  in  numbers  in  air  warfare  is  the  primary  indication  of  success, 
the  principles  of  aerial  warfare  demand  an  attack  when  there  is  the  slightest  chance  of 
success,  and  perhaps  more  than  in  other  military  branches,  a  leader's  tactical  skill  is 
the  deciding  factor  in  air  combat. 

WARFARE  ALTITUDES 

The  importance  of  altitude,  when  previously  mentioned,  referred  to  securing  the  upper  position  when 
engaging  an  enemy.  Flight  altitudes  should  be  considered  from  another  viewpoint,  i.  e.,  the  divisions  of 
flying  heights  in  accordance  with  the  mission  of  the  airplane.  Set  rules  cannot  be  made  on  this  score  as 
altitude  in  warfare  is  influenced  by  the  tactical  situation  and  atmospheric  conditions.  A  general  classifica- 
tion divides  flight  levels  into  low,  mean  and  high.  Low  altitude  includes  anything  up  to  5,000  feet ; 
offensives  against  ground  objective  being  conducted  below  2,000  feet,  and  2,500  to  3,000  feet  being  most 
favorable  for  night  operations,  bombing  and  photography.  At  mean,  height,  5,000  to  10,000  feet,  combat 
planes  have  the  most  favorable  altitude  for  tactical  missions ;  photographic,  fire-control  and  bombing 
machines  may  also  employ  these  elevations.  High  flight,  10,000  feet  and  above,  appears  best  suited  for 
combat  airplanes  in  the  aircraft  screen  and  those  seeking  to  avoid  hostile  craft  when  proceeding  on  or 
returning  from  a  mission. 

TACTICAL  SKILL 

Essentially,  military  airplanes  are  fighting  units,  not  individuals,  and  should  operate 
in  groups  or  formations,  the  strength  and  composition  of  which  are  governed  by  the 
nature  of  the  mission.  Operating  singly,  the  duties  assigned  should  be  those  which 
permit  the  craft  to  remain  within  areas  providing  support  from  other  aircraft. 

Morale,  the  feeling  of  security  and  invincibility,  contributes  largely  to  success. 
Offensives  successfully  executed  over  enemy  territory  quickly  establish  the  spirit  of 
victory  and  turn  possible  timidity  into  aggressiveness. 

The  particular  method  of  attack  which  offers  greatest  probability  of  success  is 
ordinarily  pointed  out  by  the  leader's  actions.  Parallel  attacks  head-on,  from  rear 
or  side,  give  no  advantage  to  either  adversary;  the  importance  of  gaining  the  upper 
position  has  already  been  emphasized  and  is  to  be  remembered  as  a  fundamental  tactical 
rule.  When  attacking  with  the  superior  force  the  enveloping  formation  is  frequently 
used;  circling  about  the  enemy,  the  airplanes  engaged  thus  gain  concentration  of  fire 
and  lessen  the  chances  for  escape  of  the  quarry.  Pursuit  is  a  matter  almost  entirely 
dictated  by  the  superiority  of  speed.  Here  ^again  higher  altitude  offers  the  advantage 
of  speed  acceleration  in  descent.  Once  it  is  determined  that  the  pursued  cannot  be 
overtaken  before  the  radius  of  action  is  exhausted,  or  the  chase  continued  to  dangerous 
depth  over  hostile  territory,  a  return  should  be  made.  The  escaping  plane  will 
generally  fly  directly  toward  the  sun  or  into  clouds  or  haze;  there  is  also  a  fair 
probability  that  when  nearly  overtaken  its  pilot  will  suddenly  slow  down  and  drop,  in  an 
endeavor  to  have  the  pursuer  pass  him,  thus  reversing  the  situation. 

Convoying  bombing  airplanes  is  an  important  duty  of  combat  machines.  Generally,  the  bombers 
leave  the  ground  first,  the  swifter  machines  following  some  minutes  later  and  meeting  at  the  designated 
air  rendezvous  about  the  same  time.  The  post  of  the  fast  fighters  is  above  or  on  the  flanks  of  the  forma- 
tion, flying  as  advance,  flank  and  rear  guards. 


160 


Practical    Aviation 


A  successful  attack  on  the  enemy's  tail  from  the  rear  and  slightly  below,  an  effective 
method  when  the  attacking  airplane  has  superiority  of  speed 


From  paintings  by  Lieut.   Farre 

Maneuvering  for  position  in  air  combat  above  the  clouds 


Contact   Patrol,    Armor   and    Heavy   Armament  161 

CONTACT  PATROL 

A  tactical  reconnaissance  during  the  progress  of  an  attack,  establishing 
a  liaison  between  infantry  of  the  first  line  and  their  commanders  in  the  rear, 
giving  positions  of  friendly  and  enemy  troops,  and  carrying  out  offensive 
actions  against  enemy  troops  on  the  ground — that  is  contact  patrol,  perhaps 
the  most  thrilling  task  that  comes  to  the  aviator  in  line  of  duty. 

Airplanes  assigned  to  contact  patrol  duty  arrive  over  the  front  line  trenches 
exactly  at  the  time  when  the  attack  is  scheduled  to  commence,  taking  a  position  just 
over  or  under  the  predetermined  trajectory  for  the  artillery  barrage  fire.^  The  progress 
of  the  attack  is  observed;  when  the  infantry  advances  to  its  first  objective,  its  position 
is  signaled  to  the  aviators  by  means  of  a  shutter,  lamp  or  flare.  The  position  is  traced 
on  the  pilot's  map,  which  is  placed  in  a  weighted  message  bag  with  any  necessary 
comment;  he  flies  then  to  the  infantry  headquarters,  and  coming  down  within  200  feet 
of  the  ground  drops  the  bag.  Sometimes  the  airplane's  message  is  delivered  in  tele- 
graph code  by  lamp,  Klaxon  horn  or  Very's  lights  and  sm.oke  bombs;  wireless  is 
occasionally  used,  but  offers  the  possibility  of  interception  by  the  enemy  and  is  less 
desirable.  The  reports  preferably  include  the  state  of  enemy  trenches  during  the 
attack,  troop  movements  and  location  of  any  new  trenches. 

The  offensive  action,  which  is  part  of  the  object  of  a  contact  patrol,  is  literally  a 
trench  raid  conducted  in  formation  by  combat  aircraft.  The  usual  method  is  for  the 
first  man  to  fly  along  the  line  of  the  enemy's  first-line  trench,  very  low  under  the 
barrage,  in  fact  usually  less  than  100  feet  above  the  trench  parapet.  The  second  man 
takes  the  second,  or  support  line,  both  directing  downward  a  stream  of  infilade  fire 
from  machine  guns.  It  is  the  object  of  the  second  man  to  prevent  effective  fire  at  the 
first-line  man;  the  airplanes  in  consequence  fly  almost  abreast.  Meanwhile,  the  support, 
or  third  line  trench  has  been  covered  by  a  third  airplane,  with  the  object  of  demoraliz- 
ing the  troops  in  its  shelter.  A  fourth  airplane  is  meanwhile  zig-zagging  over  the 
trenches,  combating  any  attempts  to  direct  effective  rear  fire  from  the  trenches  after 
the  machines  have  passed. 

The  speed  of  flight  of  all  four  machines  is  120  miles  an  hour  or  better,  eliminating 
the  possibility  of  accurate  aiming  by  gunners  returning  small-arms  fire  from  the 
trenches.  Anti-aircraft  guns  are  also  ineffective  at  the  low  angle.  The  density  of  the 
air  at  the  ground  and  the  powerful  types  of  airplanes  used  make  the  effect  of  wind 
puffs  or  disturbances  from  shell  bursts  negligible  on  control.  The  low  altitude  and 
high  speed  also  tends  to  make  the  airplane  rise;  to  overcome  this  the  nose  is  pointed 
slightly  downward,  pointing  the  rigid  gun  at  the  best  angle  to  rake  the  trenches. 

When  the  machine  guns  have  been  discharged  a  return  to  friendly  lines  is  made, 
a  dangerous  proceeding,  as  it  requires  flying  up  through  the  barrage  fire,  the  smoke 
from  which  screens  the  craft  from  friendly  gunners. 

ARMOR  FOR  AIRPLANES 

Armor,  mounted  in  sheets  protecting  the  airplane's  vital  parts,  or  in  the  form  of  turrets  and  shields, 
proof  against  small-arms  fire,  is  indispensable  and  practical  for  low  altitude  operations.  Armor  plate  % 
inch  in  thickness  weighs  about  10  pounds  to  the  square  foot,  making  the  weight  consideration  an  important 
one.  The  protection,  therefore,  is  generally  limited  to  armor  plate  beneath  the  motor  and  cockpit,  dis- 
position and  quantity  being  governed  by  the  type  of  airplane  and  the  height  at  which  it  is  usually  flown. 
Protection  from  overhead  fire  not  being  considered,  adequate  security  from  rifle  and  machine  gun  fire  on 
vital  portions  is  thus  gained  by  an  average  armored  area  of  30  square  feet,  or  by  an  additional  weight  of 
300  pounds.  Flying  efficiency  being  lessened  by  weight  additions,  the  heavy  armor  protection  which 
would  be  effectual  against  artillery  fire  is  eliminated  from,  calculations,  leaving  the  evasion  of  fire  to  the 
airplane's  high  speed  and  maneuvering  ability. 

Turrets  and  shields  are  furnished  for  protection  in  combat  with  hostile  airplanes,  shields  bein^f 
mounted  on  universal  joints  so  they  can  be  lowered  for  underneath  protection  when  not  required  b/ 
the  gunner. 

HEAVY    AIRPLANE   ARMAMENT 

Explosive  shells  to  be  fired  from  airplanes  have  been  successfully  adapted  to  a  specially  designed, 
light  weight  3-inch  rapid  fire  gun.  By  reason  of  the  short  ranges  used,  high  muzzle  velocity  is  not 
required  in  air  combat  and  the  great  weight  of  the  same  calibered  field  artillery  piece  may  be  cut  down 
by  elimination  of  the  long  barrel,  recoil  mechanism  and  heavy  carriage.  These  aerial  guns  in  consequence 
weigh  less  than  250  pounds.  Instead  of  employing  hydraulic  cylinders  for  the  recoil,  the  aviation  arm 
takes  up  firing  stresses  by  balanced  fire,  the  gun  having  divided  barrels,  the  projectile  being  loaded  in  the 
forward  barrel,  the  powder  charge  placed  in  a  chamber  between  it  and  a  second  barrel  which  is  loaded 
with  fine  shot.  When  the  gun  is  fired  the  fine  shot  is  discharged  backward,  its  force  balancing  in  large 
measure  that  of  the  projectile  discharging  in  the  opposite  direction.  The  slight  difference  in  force  is  the 
recoil.  Wooden  breechblocks  which  blow  out  rearward  are  also  used. 

Heavy  aircraft  armament  is  used  on  airplanes  of  the  super-plane  class  where  lifting  capacities  of  4 
tons  are  usual.  The  3-inch  and  2-pounder  airplane  guns  do  not  have  the  high  accuracy  of  fire  which  is 
essential  to  field  artillery  pieces  and  given  by  their  higher  firing  velocities.  Accuracy  and  high  striking 
velocity  is  of  less  importance  against  aircraft,  for  the  reason  that  high  explosives  can  cause  the  collapse 
of  an  airplane  without  actual  contact  with  it. 


162 


Practical    Aviation 


British    Official    Photo 

Crew  of  an  anti-aircraft  battery  securing  ranging  data 
ANTI-AIRCRAFT  FIRE 

The  most  common  trap  which  the  aviator  falls  into  is  in  diving  to  low  altitudes 
over  hostile  territory  and  coming  within  range  of  anti-aircraft  batteries.  These  dives 
may  be  occasioned  by  following  an  enemy  airplane  downward  in  heat  of  combat,  or 
seeking  to  escape  from  a  larger  hostile  air  force.  Deliberate  luring  of  airplanes  to 
altitudes  within  range  of  anti-aircraft  fire  is  also  a  regular  practice  in  warfare.  Attacks 
on  balloons  and  bombing  expeditions  on  enemy  bases  also  subject  the  military  flier  to 
this  defensive  fire  from  the  ground.  An  understanding  of  anti-aircraft  guns  is  valuable. 
ACTION  UNDER  FIRE 

The  aviator  under  attack  observes  the  effect  of  range  fire  directed  at  him  by  the 
white  smoke  of  the  shell  bursts,  termed  "cream  puffs."  When  the  sound  of  the  burst 
can  be  heard  above  the  noise  from  his  airplane  motor  it  may  be  accepted  that  the 
gunners  are  getting  the  range  with  dangerous  accuracy.  An  escape  is  then,  in  order. 
If  diving  or  climbing  is  attempted  the  gunner  may  lower  or  raise  his  fire  and  estimate 
the  airplane's  velocity  with  fair  accuracy.  Perhaps  the  best  method  of  escape  is  to 
employ  the  pancake,  throttling  the  motor  and  dropping  several  hundred  feet;  this 
maneuver  is  difficult  of  detection  from  the  ground,  as  the  machine  remains  horizontal 
to  its  original  position.  Zig-zag  flight  ahead  at  high  speed  is  then  usually  employed, 
although  the  straight  course  is  a  valuable  variation  because  of  its  unexpectedness. 
All  forms  of  aerobatics  are  frequently  used  when  the  shells  are  dangerously  close. 

Anti-aircraft  artillery  loses  its  accuracy  of  aim  when  the  airplane  is  at  elevations 
greater  than  9,000  feet,  although  a  chance  hit  may  be  expected.  Shrapnel  is  less  dan- 
gerous than  high  explosive  shelling  as  a  hit  from  its  scattered  fire  must  strike  a  vital 
part  to  be  effective;  explosive  shells  do  not  necessarily  have  to  reach  the  target,  how- 
ever, as  the  light  structure  of  a  wing  may  be  crushed  by  detonation  in  a  near  vicinity. 
The  principal  object  of  anti-aircraft  fire  is  to  force  the  airplane  to  greater  altitudes, 
and  while  the  percentage  of  hits  is  relatively  small,  the  guns  are  sometimes  amazingly 
effective  at  low  elevations  and  the  aviator's  safety  lies  in  climbing  out  of  range. 
LOCATION  AND  TYPES  pF  GUNS 

Both  fixed  and  mobile  anti-aircraft  artillery  is  well  concealed  by  pits  and  camouflage 
from  hostile  airmen.  The  guns  are  of  two  types;  important  positions  are  usually 
defended  by  high  power  guns  on  fixed  emplacements  of  concrete;  the  principal,  and 
largest  class,  comprise  light  rapid-fire  pieces,  1,  \l/2  or  2-pounders,  and  heavier  types 
up  to  6-pounders.  mounted  on  motor  trucks  of  a  special  type.  The  heavy  guns  are 
generally  used  at  headquarters  of  commanding  generals  of  army  corps,  the  lighter 
types  being  assigned  to  brigades  and  divisions  in  the  field.  While  highly  mobile,  the 
guns  are  usually  placed  at  supporting  distance,  about  1,000  yards  apart.  They  have 
high  muzzle  velocity  and  consequent  long  range,  firing  projectiles  with  combination 
percussion  and  time  fuses,  explosive  and  incendiary  charges.  Automatic  sights  are 
used  with  graduated  altitude,  drift  and  deflection  scales  designed  for  high  angle  fire, 
45  to  75  degrees.  Fire  correction  is  obtained  by  use  of  special  projectiles  giving  off 
varying  densities  of  smoke. 


Pointers    on    Anti-Aircraft    Fire  163 


British   Official    Photo 

Mobile  anti-aircraft  guns  mounted  on  motor  trucks 

SHELL  TRAJECTORIES  AND  BALLISTICS 

The  trajectory,  or  path  described  by  a  projectile,  is  influenced  by  gravity  and  time  or 
resistance  of  the  air.  In  anti-aircraft  firing  the  line  of  sight  is  at  angles  up  to  90  degrees 
and  seldom  less  than  15  degrees,  consequently  the  trajectory  is  unsteady  and  can  only  be 
aided  in  comparatively  small  degree  by  high  velocity.  Velocity  losses  as  high  altitudes 
are  reached  also  serve  to  magnify  small,  errors  in  aiming,  which  in  turn  are  liable  to 
frequent  occurrence  because  of  the  short  time  allowed  for  computations. 

A  further  contribution  to  inaccuracy  is  found  in  the  changes  in  air  density  as  altitude 
increases,  affecting  the  ballistics  of  the  shell.  Time  fuses  for  this  reason  burn  erratically, 
wide  variations  in  rate  making  them  unsatisfactory ;  the  frail  nature  of  the  airplane  miti- 
gates against  the  operation  of  percussion  fuses  also,  even  though  the  projectile  pass  directly 
through  the  target.  The  percussion  type  does  not  explode  unless  it  reaches  its  target  and 
is  therefore  valueless  for  furnishing  firing  data. 

Firing  by  salvo  is  considered  the  best  method,   four  guns  being  arranged  in  a  square 
at  200-foot  intervals  with  the  observer  in  the  center.     They  are  all  aimed   with  the  samje 
firing  data,  a  bracket  being  thus  obtained  on  which  corrections  are  based. 
DEFENDING  POSITIONS 

Aviators  must  not  underestimate  the  danger  from  anti-aircraft  fire;  improvements 
are  constantly  being  made  and  the  exercise  of  proper  caution  is  required,  particularly 
in  raiding  defended  positions. 

Outpost  detector  stations  may  be  expected,  equipped  with  microphones  and  other  forms 
of  electrical  sound  amplifiers  which  detect  the  approach  of  hostile  aircraft  at  considerable 
distances.  Telescopes  and  long  range  glasses  sweep  the  skies  constantly  and  powerful 
searchlights,  fixed  and  mobile,  are  ready  at  night  to  throw  a  revealing  beam  on  the  invader. 
The  outpost  stations  are  also  equipped  with  anti-aircraft  batteries  and  combat  airplanes 
which  take  to  the  air  at  the  first  warning  of  an  enemy  approach. 

The  line  of  interior  defense  ordinarily  extends  in  a  circle  of  four-gun  groups  placed 
at  1,000-yard  intervals  on  a  diameter  of  five  or  more  miles  from  the  defended  position. 
These  defenses  must  be  passed  before  the  objective  is  reached,  when  a  fierce  fire  and 
engagement  by  combat  craft  may  also  be  expected. 

ATTACKS  ON  BALLOONS 

Captive  balloons  used  for  observation  and  regulating  artillery  fire  are  most  dangerous  to  attack. 
These  helpless-appearing  gas  bags  are  about  200  feet  long-  by  30  feet  diameter,  placed  about  2  miles  apart 
at  an  altitude  of  4,000  feet.  They  are  protected  by  several  fast  combat  airplanes  which  circle  above  them, 
and  an  attack  means  flying  through  a  heavy  anti-aircraft  barrage  as  well.  Amazing  accuracy  is  often 
attained  by  anti-aircraft  gunners  at  the  4,000-foot  altitude  and  the  best  are  assigned  to  balloon  protection. 

One  of  the  most  successful  methods  of  attack  is  for  the  hostile  airplane  to  fly  beyond  the  balloon's 
position  at  a  minimum  altitude  of  6,000  feet,  circling  back  over  it  and  diving  with  the  motor  cut  off,  so 
it  cannot  be  heard.  The  dive  for  1,500  feet  should  be  steep  with  the  machine  in  almost  vertical  position 
then  slightly  lessening  the  angle  so  a  raking  fire  may  be  delivered  when  within  200  feet.  If  the  tracer 
bullets  show  the  mark  has  been  reached,  the  attacker  should  swerve  in  a  wide  arc  to  avoid  the  effects 
of  the  explosion.  After  delivering  gun  fire  quick  climb  is  usually  required  to  avoid  the  pursuing  airplane 
guards  and  the  shelling  from  the  ground. 


164 


Practical    Aviation 


> 


WA. 


Bombing  Crews,  Planes  and  Training  Courses  165 

BOMBING  AIR  RAIDS 

Destruction  of  enemy  bases  and  headquarters,  factories,  warehouses  and 
magazines,  railroads  and  bridges,  is  the  duty  of  specially  trained  bombers. 
The  bombing  arm  of  the  air  service,  once  a  matter  of  a  few  volunteers  operat- 
ing independently,  has  now  assumed  the  proportion  of  about  one-quarter  of 
the  total  air  force,  operating  in  squadrons  of  12  airplanes  each.  Large  groups, 
consisting  of  several  squadrons,  generally  conduct  bombing  raids,  escorted 
over  the  lines  by  fast  fighting  squadrons,  which  do  not  continue  to  the 
objective  owing  to  limited  fuel  capacity.  Numerical  increase  in  airplanes 
for  bombing  is  based  upon  the  division  of  defensive  fire  thus  required  of 
anti-aircraft  batteries. 

TYPES  OF  BOMBING  AIRPLANES 

Examination  of  the  various  airplanes  employed  for  bombing  reveals  wide  diversity  in 
type,  but  selection  according  to  long  cruising  radius  and  weight-carrying  capacity.  In 
triplane  construction,  machines  with  3  motors,  2  tractor  and  1  pusher  propellers  are  of  two 
types,  large  and  small,  the  greater  having  a  bomb  carrying  capacity  up  to  5  tons.  A  small 
single-seater  triplane  is  occasionally  used.  In  biplane  types,  motor  power  up  to  600  h.p. 
is  found,  with  100-foot  wing  spreads,  2  or  3  motors  and  one  or  more  guns.  The  single 
motor,  two-seater,  is  also  used.  There  are  day  machines  and  night  machines  in  the  aerial 
bombing  arm,  the  characteristics  of  the  night  airplanes  showing  moderate  speed  and  slow 
climb,  but  great  inherent  stability. 

Night  air  fighting  is  almost  unknown,  so  speed  and  maneuvering  ability  are  secondary 
to  capacity  for  carrying  explosives. 

MUFFLERS  AND  FLARES 

Since  the  objectives  of  bombing  squadrons  are  almost  without  exception  fortified 
positions,  the  anti-aircraft  batteries  are  the  principal  sources  of  danger.  In  daylight 
raids,  the  enemy  combat  airplanes  are  a  material  menace,  but  their  effectiveness  is  large- 
ly reduced  in  the  dark  or  in  the  uncertain  glare  of  searchlights.  Silencing  the  noise  of 
airplane  engines  by  elimination  of  the  exhaust  sounds  which  enemy  microphones  detect 
miles  away,  requires  added  weight  and  loss  of  power,  as  against  the  lesser  weight  of 
additional  fuel  required  for  higher  altitude  flight. 

For  night  air  operations  parachute  flares  are  used.  These  are  dropped  from  the  air- 
planes and  light  up  a  circular  area  \l/>  miles  in  diameter  with  400,000  candle  power 
illumination.  Buildings,  gun  emplacements,  railroads,  wagon  trains,  troops  or  ammuni- 
tion dumps  are  thus  clearly  revealed  and  the  particular  target  easily  selected.  Suspended 
by  the  parachute  at  a  height  of  1,500  to  2,000  feet,  these  flares  also  materially  interfere 
with  careful  aiming  of  anti-aircraft  guns,  since  the  attacking  airplanes  are  in  the  darkened 
area  well  above  the  light  from  the  flares. 

TRAINING  BOMBING  CREWS 

Training  a  bombing  crew,  i.  e.,  a  pilot  and  a  bomber,  consists  of  highly  specialized 
instruction  in  flying,  navigation,  fighting,  aiming  and  firing.  The  men  are  selected 
from  those  of  highest  standing  in  the  ground  school  classes. 

The  preparatory  stage  of  instruction  brings  the  bombers  together  with  pilots,  who 
have  mastered  acrobatic,  cross-country  and  formation  flying.  A  week  is  devoted  to  study 
of  the  theory  of  bombing,  explosives  and  sighting  devices.  Flights  are  then  taken  over 
courses  marked  by  camera  obscuras  and  Batchelor  mirrors  located  on  housetops,  instru- 
ments by  which  the  course  of  the  airplanes  flying  over  them  can  be  traced  on  charts  with 
the  slightest  errors  of  the  crew  shown.  Instructors  correct  these  errors  and  shift  the 
crews  around  until  the  best  combinations  in  pairing  are  secured. 

Bomb-dropping  is  the  next  stage  of  the  training.  A  painted  circle  with  a  25-foot 
radius  is  the  target,  the  bomb  being  a  plaster-of-Paris  missile,  accurately  balanced  and 
weighted.  Low  altitude  flight  is  followed  by  target  practice  at  3,000  and  4,000  feet  until 
an  average  score  of  seven  hits  out  of  ten  bombs  dropped  is  recorded.  The  training  is  then 
continued  at  elevations  between  6,000  and  12,000  feet.  The  size  of  the  target  is  not  changed 
even  when  the  'flight  elevation  is  two  miles  above  the  earth,  at  which  height  the  painted 
disc  looks  like  a  flyspeck.  Moving  targets  are  also  used,  these  taking  the  form  of  dummy 
trains  and  individual  objects. 

The  final  stage  in  bombing  training  includes  photographing  of  assumed  enemy  objec- 
tives and  night  raiding.  Aerial  gunnery,  with  fixed  and  movable  machine  guns,  is  also 
thoroughly  mastered. 


166 


Practical    Aviation 


<  Rubbereye 
piece 


Large  high  explosive  loml 
used  by  super-planes 


Direct /on  of  mof/or, 


Movob/e  po/nfer 
for 


With  airplane  sta/'/o/7ary\ 

ago/nsf  Aeod  w/ncf. j 

Aqainsf  ansfonf  head wrxf 
Aga/nsf  head  w/nd  A'-.. 
Ntt/i  wr?d at  A  .... 
Without  w/nd 
With  ivmd...  "-• 


.Dish  opera f/hg 
'     prism    " 


Universal 
joint 


Movable 
prism  •. 


Prism  pivot 


8     C 


Figure    136 — Effect   of   air  resistance   and  gravity 
on   bomb    trajectories 


137 — A   type  of  telescopic 
ran^c   finder 


BOMB  DROPPING 

A  bomb  released  from  an  airplane  describes  a  curved  path  in  its  fall;  this  flight  path,  or  trajectory, 
must  be  determined  and  practically  applied  if  accuracy  is  to  be  attained.  Velocity  of  the  airplane  and 
its  height  from  the  ground  determine  how  far  in  advance  of  the  target  the  bomb  must  be  released,  for 
the  distance  the  missile  will  carry  increases  with  the  airplane's  velocity  and  height  increases. 

The  bomb  is  subjected  to  air  resistance  and  gravity  forces  ;  if  it  were  dropped  from  a  stationary  point 
in  a  vacuum  its  trajectory  would  be  vertical  as  the  dotted  line  in  Figure  136.  Dropped  from  an  airplane 
in  motion,  however,  it  is  given  an  initial  speed  equal  to,  and  in  the  same  direction  as  the  motion.  In  its 
fall  it  is  ordinarily  subjected  to  the  force  of  wind  in  motion.  The  various  flight  paths  shown  in  Figure  136 
illustrate  the  wind's  effect  on  the  fall  with  the  airplane  stationary  or  in  motion.  Trajectories  A-B  and  A-D 
are  with  the  wind  and  the  airplane  in  motion,  A-C  with  no  wind,  but  airplane  moving,  A-D,  A-D'  and  A-E, 
with  the  machine  flying  against  the  wind ;  path  A-F  shows  a  head  wind's  action  on  a  bomb  released  from 
aircraft  theoretically  without  motion. 

It  is  immediately  evident,  then,  that  knowledge  of  the  velocities  of  airplane  and  wind  are  required. 
Best  results  in  bomb  dropping  are  obtained  by  releasing  the  projectile  into,  or  against,  the  wind,  and 
the  wind  velocity  is  easily  determined  by  calculating  the  difference  between  the  normal  velocity  of  the 
airplane  and  its  velocity  with  respect  to  the  earth  at  the  given  time.  Thus  if  an  airplane  having  a  normal 
speed  of  90  m.p.h.  is  found  to  be  flying  only  70  m.p.h.  with  reference  to  the  earth,  then  the  resistance  of 
the  head  wind  is  90 — 70  =  20  m.p.h.  It  then  appears  only  necessary  to  know  the  airplane's  altitude  and 
the  initial  velocity  of  the  bomb  to  determine  the  trajectory. 

Mathematical  calculations  are  only  estimates,  however,  due  to  the  fact  that  they  are  based  on  the 
supposition  that  the  wind  is  a  constant  force  at  all  altitudes  between  the  airplane  and  the  ground, 
whereas  it  is  well  known  that  wind  velocity  varies  at  different  altitudes  and  changes  direction  appreci- 
ably by  veering.  So  while  it  appears  comparatively  easy  to  construct  a  table  of  velocities  and  alti- 
tudes to  give  the  exact  instant  when  a  bomb  should  be  released  to  hit  the  target,  the  ideal  range  finder 
awaits  the  day  when  the  laws  governing  the  capricious  action  of  winds  are  fully  understood. 

RANGE  FINDERS' 

Instruments  with  telescopic  sights  have  appeared  in  several  forms  in  military  aviation.  Probably  the 
best  type  is  illustrated  in  Figure  137.  The  telescope  remains  vertical,  but  the  prism  mounted  in  the  base 
is  controlled  by  a  graduated  disk.  There  are  two  indexes  on  the  disk,  one  of  which  corresponds  to  the 
vertical  speed,  or  dead  point  of  the  range  finder,  and  the  other  to  the  vision  of  22°  30'.  Another  index, 
fixed  to  the  body  of  the  range  finder,  serves  as  a  basis.  At  0°  the  marksman  views  the  ground  along  the 
vertical  (B  in  Figure  137)  ;  at  22°  30'  the  inclination  of  the  visual  ray  is  that  angle  (C)  in  front  of  the 
airplane;  at  5°  the  inclination  is  as  A,  or  5°  behind  the  airplane.  A  small  movable  index  is  attached  to 
the  disk,  but  is  fixed  by  a  small  stop.  Therefore,  when  the  index,  fixed  on  a  graduation  of  the  disk, 
passes  the  dead  point  it  falls  into  a  small  notch,  thus  informing  the  marksman  that  he  is  viewing  the 
ground  according  to  the  inclination  which  he  had  marked. 

There  is  a  spirit  level  in  the  body  of  the  telescope  so  arranged  that  the  edges  of  the  air  bubble  are 
refracted  as  a  black  circle,  serving  as  a  sighting  center.  While  range  finding,  this  bubble  must  be  kept 
in  the  center  of  the  eye  piece  so  the  telescope  remains  vertical  with  the  ground,  irrespective  of  the  air- 
plane's angle  of  inclination. 

A  universal  joint  permits  the  free  inclination  of  the  range  finder,  but  when  the  visual  ray  is  accidentally 
directed  to  right  or  left,  instead  of  front  or  rear  of  the  route,  an  electric  route  corrector,  acting  upon  a 
very  sensitive  galvanometer,  indicates  the  necessary  correction  to  regain  the  route. 


Bomb    Dropping    and    Range    Finding 


167 


U.    Photo. 

Drawing  of  a  German  airplane  showing  bomb  dropping  mechanism 

OPERATION  OF  THE  RANGE  FINDER— Height  is  obtained  by  subtracting  the  height  of  the 
objective  from  the  altitude  indicated  by  the  altimeter.  Thus,  if  the  airplane  is  flying  at  5,000  feet  and 
seeks  to  bombard  a  100  foot  building  the  height  will  be  5,000 — 100  =  4,900  feet. 

A  few  minutes  before  arriving  over  the  bombardment  objective  the  two  elements  are  found  which  are 
necessary  to  read  on  the  chart  the  proper  firing  angle.  The  index  on  the  graduated  disk  is  set  at  22°  30'. 
The  range  of  some  point  forward  on  the  ground,  such  as  a  house  or  edge  of  a  wood,  is  found.  This  point 
is  caught  in  the  circle  formed  by  the  spirit  level's  air  bubble  and  followed  while  turning  the  disk  until 
the  index  falls  into  the  notch  at  the  dead  point;  at  this  instant  the  chronograph  is  released  and  the  point 
is  followed  in  the  range  finder  until  0°  of  the  disk  checks  with  the  dead  point,  when  the  chronograph  is 
instantly  stopped.  The  resultant  number  of  seconds  of  time  given,  when  found  on  the  chart  in  the  line  of 
altitude  indicates  the  airplane's  speed  with  reference  to  the  ground  and  the  proper  sighting  angle  in  degrees. 
The  index  is  immediately  set  at  this  angle  and  the  bomber  is  ready  to  operate.  The  range  finder  is  trained 
on  the  target  when  within  a  mile  or  two  of  it,  and  at  the  instant  when  the  index  fixed  at  the  proper 
number  of  degrees  falls  into  the  dead  point,  the  bombs  are  released. 


168 


Practical    Aviation 


Handle, 


Revolving  vane 


Stabilizing  fin 


Parachute      Locking 
'cords          spindle 


Inflammable 
rope  Mapping 


Firing  pin 
Percussion  cap 


Mease  lever^ 


Stabilizing  fin        Tailpiece 

— Spring 


— -Hammer 


firing  charge 

Explosive 


Point  of 'pilot rod 

Fig.  138 — Incendiary  bomb  Figs.  139,  140,  141 — Three  types  of  explosive  bombs 

TYPES  OF  BOMBS 

Bombs  for  use  against  hostile  forces  may  be  roughly  classed  as  (a)  explosive, 
(b)  incendiary.  There  are  also  smoke  bombs  for  signaling  and  for  smoke  screens, 
rockets  for  attacking  balloons,  flare  rockets  for  illuminating  positions  and  steel  darts 
for  use  against  enemy  personnel.  Incendiary  and  explosive  bombs  will  be  briefly 
described. 
INCENDIARY  BOMBS 

The  bomb  illustrated  in  part  section  in  Figure  138  is  of  the  type  used  for  setting 
afire  towns  and  military  depots.  Its  metal  base  diameter  is  about  10  inches.  From  this 
cup  base  a  hollow  metal  funnel  runs  through  the  center  to  the  handle;  this  is  filled  with 
thermite,  a  composition  of  finely  divided  aluminum  and  a  metallic  oxid,  which  on 
ignition  produces  heat  so  intense  as  to  melt  steel.  A  great  flare  of  light  is  thrown  off 
by  the  thermite,  its  heat  quickly  melting  the  funnel;  the  molten  metal  spreads  rapidly 
as  the  bomb  strikes  and  sets  up  at  once  a  fierce  fire  if  it  strikes  any  combustible  material. 

.  Another  form  of  incendiary  bomb  contains  a  gasoline  tank  mounted  on  an  arrow  shaft  which,  when 
the  arrow  point  strikes,  sets  in  motion  a  wheel  which  rotates  against  a  ferro-cerium  brush,  the  friction 
generating  a  stream  of  sparks  which  ignites  the  gasoline.  A  powder  charge  is  also  exploded,  which  increases 
the  rate  of  burning.  Fins  maintain  steadiness  in  flight  and  barbs  are  attached  for  arresting  the  arrow's 
flight  when  used  against  airships. 
SAFETY  DEVICES 

Airplane  bombs  have  three  safety  devices;  safety  pin,  wind  wheel,  and  fuse  device,  usually  a  com- 
pression spring  or  resistance  split  ring.  Safety  pins  are  pulled  before  the  bombs  are  released;  wind 
wheels  or  revolving  vanes  usually  act  in  less  than  100  feet,  preparing  the  firing  pin  for  action  on  impact. 

EXPLOSIVE  BOMBS 

In  the  illustrations  above  three  types  of  aircraft  bombs  carrying  explosive  charges 
are  clearly  pictured  in  section.  The  action  of  their  safety  devices  and  firing  mechanism 
will  be  described. 

Figure  139 — The  safety  device  is  operated  by  the  centrifugal  forces  during  the  fall,  the  revolving 
vane  giving  the  bomb  a  rotary  motion.  The  firing  charge  and  detonator,  placed  in  the  nose  of  the  bomb, 
are  held  separate  from  the  firing  pin  by  means  of  two  spring-loaded  masses.  With  increase  in  centrifugal 
force  to  a  predetermined  point  the  force  of  the  springs  is  overcome  and  the  firing  charge  is  free,  excepting 
for  two  clamps  which  hold  it  in  place.  On  impact  with  the  ground  these  give  away  and  the  charge  is 
driven  into  the  firing  pin. 

Figure  140— This  is  a  somewhat  similar  type  of  bomb  with  a  firing  mechanism  also  actuated  by  direct 
impact.  Friction  firing  caps  ignite  the  fuse.  This  illustration  shows  in  detail  how  the  spring  is  held  in 
check  by  the  safety  spindle,  or  pin,  having  ball  bearings  for  easy  removal  before  the  bomb  is  released. 

Figure  141 — The  pilot  rod  in  this  type  of  bomb  rests  in  a  guide  which  keeps  it  from  sliding  until 
it  is  unlocked.  Thus  the  firing  charge  is  kept  apart  from  the  explosive  charge,  minimizing  the  danger  from 
accidental  discharge.  Stabilizing  fins  are  mounted  on  the  tail  piece. 

The  horizontal  suspension  of  the  bomb  from  the  airplane  is  shown  in  the  upper  view.  The  release 
lever  automatically  removes  the  safety  lock  and  as  the  bomb  gradually  assumes  the  vertical  position  the 
pilot  rod  slides  forward,  carrying  the  firing  charge  into  the  center  of  the  explosive  charge.  The  firing  pin 
then  slides  into  position  and  when  the  nose  of  the  bomb  strikes  the  ground  the  pilot  rod  is  driven  back 
in  its  guide,  bringing  the  firing  charge  in  contact  with  the  pin  and  percussion  cap.  The  explosion  follows. 
To  make  certain  the  sliding  forward  of  the  pilot  rod  the  fall  of  the  bomb  is  retarded  by  a  parachute. 
Telescopic  tubes  are  substituted  for  the  pilot  rod  in  some  models  of  this  bomb,  opening  to  their  full 
length  under  the  speed  of  the  fall. 
BOMB  CARRIERS  AND  LAUNCHING  CRADLES 

Clusters,   or  racks,  are  used   to  carry  bombs,   ordinarily   consisting  of   six  or  more  bombs.      The  usual 
launching  cradle  is  composed  of  two  sets  of  metal  fingers,  "hinged  at  the  top  and  pinned  at  the  bottom. 
STEEL  DARTS 

Pointed  steel  spindles  with  spiralled  tails  to  give  a  rotary  motion  and  steadiness  in  flight  are  used 
against  massed  troops.  From  ISO  to  200  are  released  at  a  time.  They  are  non-explosive. 


Practical    Aviation  169 


REVIEW  QUIZ 

Aerial  Gunnery  and  Combat— Bombs  and  Bombing 

1.  Give  the  essential  differences  between  patrolling  and  sentinel  duty 

for  combat  airplanes. 

2.  What  effect  has  technical  superiority  of  airplane  and  armament? 

Compare  pusher  and  tractor  types  for  points  of  combat  su- 
periority. 

3.  Explain  why  knowledge  of  the  appearance  of  enemy  types  of  air- 

plane is  valuable,  how  clouds  and  sun  are  valued  in  attack, 
why  knowledge  of  aerobacy  is  essential. 

4.  Describe  the  operation  of  the  Lewis  machine  gun  in  detail;  begin- 

ning with  loading,  state  the  successive  operation  of  the  mechan- 
ism ;  explain  how  the  magazine  feeds,  the  ejector  operates  and 
how  power  is  developed  by  the  cartridges  for  successive  cycles 
of  operation. 

5.  Under  what  conditions  of  equality  of  equipment  may  gunnery  skill 

become  the  deciding  factor  in  combat? 

6.  Why  is  high  rate  of  fire  essential  to  an  airplane  arm? 

7.  Describe  five  common  types  of  bullets  used  in  aerial  warfare  and 

give  the  function  of  each. 

8.  Compare  the  relative  advantages  of  mounting  machine  guns  rigidly 

on  the  upper  plane  and  placing  them  to  fire  through  the  pro- 
peller. How  is  the  latter  accomplished? 

9.  By   several  illustrations   of  machine   gun  arrangement  show  how 

effective  angle  of  fire  may  be  increased. 

10.  There  are  ten  principles  by  which  skill  in  attack  may  be  acquired. 

State  them. 

11.  What  is  the  best  method  of  escape  for  a  single  machine  attacked 

by  a  hostile  formation? 

12.  Explain  how  captive  observation  balloons  are  protected  and  describe 

a  method  of  attack. 

13.  State  two  reasons  why  the  V-shaped  arrangement  is  preferred  for 

flying  in  formation. 

14.  Explain  how  a  turn  to  the  left  is  executed ;  describe  how  the  leader 

signals  attention  and  approach  of  hostile  aircraft. 

15.  Show  by  a  mathematical  calculation  under  the  N-Square  Law  how 

superior  tactics  may  cause  the  defeat  of  a  numerically  superior 
force. 

16.  Classify  flying  heights  into  low,  mean  and  high  levels,  and  state 

how  these  apply  to  the  various  missions  of  aircraft. 

17.  What  is  contact  patrol  and  how  does  it  differ  from  combat  air 

patrols? 

18.  When  under  fire  from   anti-aircraft   batteries   what  indicates  that 

the  gunners  are  getting  the  range?    How  is  escape  best  effected? 

19.  What  forces  tend  to  destroy  the  accuracy  of  fall  of  a  bomb  dropped 

from  an  airplane? 

20.  Describe  a  type  of  incendiary  bomb,  an  explosive  bomb  and  a  safety 

device. 


170  Practical    Aviation 


CHAPTER   ANALYSIS 

Reconnaissance  and  Fire  Spotting 

RECONNAISSANCE   BY    AIRPLANE: 

(a)  Orders  for  Reconnaissance   Flights. 

(b)  Preparations. 

(c)  Gathering  Information. 

(d)  Tactical  Reconnaissance. 

(e)  Estimates  of  Enemy  Strength. 

(f)  Strategical  Reconnaissance. 

(g)  Preparatory  Reconnaissance. 
(h)  Reports  of  Flights. 

INSTRUCTION    IN    CODE    TELEGRAPHING: 

(a)  The  Code. 

(b)  Memorizing  the  Code. 

(c)  Proper  Grip  on  the  Key. 

(d)  Sending. 

(e)  Receiving. 

(f)  Visual    Signaling. 

(g)  Proficiency  Required. 

DIRECTING   ARTILLERY    FIRE: 

(a)  General  Considerations. 

(b)  Types  of  Shells. 

(c)  Ranging. 

(d)  Observer's  Map  and  Code  Signals. 

(e)  Signals  from  the  Ground. 

(f)  Method  of  Training. 

RADIO  (WIRELESS)  TELEGRAPHY: 

(a)  Theory  of  Radio  Transmission. 

(b)  Operations  in  the  Circuits. 

(c)  Radio   Receivers. 

AIRPLANE   RADIO    APPARATUS: 

(a)  Generating  the  Flectrical  Power. 

(b)  Regulating  the  Power  Output. 

(c)  Transforming  the  Energy. 

(d)  Controlling  the  Length  of  the  Radiated  Wave. 

AERIAL   PHOTOGRAPHY: 


(a) 
(b) 


The  Camera  and  Its  Parts. 
Arrangement  of  Cameras. 

(c)  Photographic   Flights. 

(d)  Mapping  from  Photographs. 


CHAPTER    XV 

. 

Reconnaissance  and  Fire  Spotting 

Reconnaissance,  the  military  term  for  the  duty  of  gathering  information 
in  the  field,  represents  a  large  share  of  the  duties  assigned  to  the  service  of 
aircraft.  In  fact,  the  utility  of  the  airplane  for  this  work  may  be  said  to 
represent  its  chief  value  in  warfare.  Offensives  in  the  air  are  mainly  defen- 
sive measures  to  prevent  enemy  reconnaissance,  and  raiding  by  bombing 
and  in  co-operation  with  land  forces  in  attack,  are  subsidiary  in  importance. 
By  and  large,  the  air  forces  are,  and  will  remain,  scouts  and  informers  for 
commanding  officers  of  troops  engaged  in  land  warfare. 

All  military  aviators  are  charged  with  reconnaissance;  no  matter  what 
their  duties  may  be,  while  HI  flight  they  are  required  to  collect  all  obtainable 
information  of  military  value. 

Aerial  reconnaissance  presents  features  Vviiich  are  primarily  for  specialists, 
for  gathering  information  of  strategical  and  tactical  value  is  accomplished 
by  devices  and  methods  mastered  only  by  careful  study.  Artillery  control, 
or  fire  spotting,  is  also  not  a  task  for  the  novice,  and  specially  trained  men 
are  required.  These  soldiers  of  the  air  are  known  as  observers,  and  in 
addition  to  textbook  and  class-room  study  courses,  they  undergo  special 
training  under  flight  conditions.  The  latter  course  begins  with  visibility 
tests  in  clear  weather  by  naked  eye,  use  of  field  glasses  and  identification  of 
known  objectives  and  their  comparative  sizes  from  successive  heights  of 
1,500,  2,000  and  3,000  feet.  These  observations  are  then  repeated  in  unfavor- 
able atmosphere,  flying  in,  below  and  above  broken  cloud  formations.  The 
altitude  is  then  increased  to  5,000  feet;  buildings  and  structures  at  a  given 
point  are  sketched  on  an  incomplete  map.  All  roads,  trails,  bridges  and 
docks  within  a  given  area  must  then  be  recorded  on  the  map,  the  tests  being 
repeated  at  flight  altitudes  of  6,000  and  8,000  feet.  Higher  altitudes,  9,000 
and  10,000  feet  are  then  sought.  Photographic  flights  are  made,  flight  orders 
and  reports  are  prepared  and  a  military  reconnaissance  made  over  an  ex- 
tended area.  Signaling  to  and  from  the  ground  is  then  practiced  and  control 
of  artillery  fire  mastered.  The  flying  course  ends  with  tests  showing  ability 
to  use  the  machine  gun  effectively  at  targets  while  in  flight.  When  the 
observer  has  completed  the  course  he  is  able  to  identify  and  give  the  pro- 
portions of  the  following  objects:  buildings,  roads,  bridges,  wharves  and 
docks,  airdromes,  aircraft  on  the  ground,  trendies,  troops,  motor  cars,  wagons 
and  artillery,  gun  emplacements,  mine  fields  and  shell  bursts  by  color  and 
by  patterns. 

Aside  from  manipulation  of  radio  (wireless)  apparatus,  the  observer  must  also 
acquire  proficiency  in  sending  and  receiving  visual  signals,  made  by  lantern,  helio- 
graph, searchlight,  rockets  and  the  Very  pistol,  all  communicated  by  dot  and  dash 
code.  Great  technical  skill  with  apparatus  and  high  speed  communication  is  not 
required,  but  the  diversity  of  subjects  requires  the  observer  to  be  of  a  good  order 
of  intelligence  with  highly  developed  powers  of  concentration. 

171 


172  Practical    Aviation 


RECONNAISSANCE   BY    AIRPLANE 

Reconnaissance  by  airplane  has  three  distinct  classifications:  (a)  tactical,  or  the 
gathering  of  detailed  military  information  in  a  limited  area  while  troops  are  engaged 
in  combat;  (b)  strategical,  or  securing  of  information  and  general  military  impressions 
over  an  extended  theatre  of  operations;  (c)  observations  for  control  of  artillery  fire. 
The  last  is  actually  a  separate  duty,  but  is  so  closely  related  to  reconnaissance  that  it 
is  best  included  under  that  broad  head. 

ORDERS   FOR   RECONNAISSANCE   FLIGHTS 

Orders  for  a  flight  may  originate  with  the  headquarters  staff  or  the  squadron  commander,  and  are 
preferably  written.  They  contain  the  serial  tactical  number  of  the  flight;  the  airplanes,  pilots  and 
observers  to  participate ;  the  time,  place  and  route,  and  the  mission  to  be  performed.  How,  when  and 
where  the  report  is  to  be  delivered  and  its  nature,  is  stated.  Ordinarily,  the  orders  are  issued  sufficiently 
early  so  pilot  and  observer  may  make  a  preliminary  study  of  the  situation. 

PREPARATIONS 

Pilot  and  observer,  generally  a  pair  accustomed  to  working  together,  immediately 
on  receipt  of  orders  consult  together  as  to  the  best  manner  of  fulfilling  the  mission. 
Route  calculations  are  made  from  the  map,  the  pilot  makes  a  test  and  final  inspection 
of  his  machine  and  the  observer  insures  that  signaling  apparatus,  note  paper,  pencils, 
weighted  message  bag,  field  glass,  watch,  camera  and  all  necessary  aids  are  included 
in  his  equipment.  The  speaking  tube,  or  aviaphone,  for  their  intercommunication  is 
made  ready,  and  a  simple  code  of  signals  arranged. 
GATHERING  INFORMATION 

The  observer's  logical  position  in  the  airplane  is  the  front  one,  enabling  the  pilot 
to  easily  watch  his  signals.  When  the  stated  objective,  or  a  position  showing  activity 
of  military  interest,  is  reached,  the  pilot  manipulates  his  controls  so  the  best  possible 
view  is  afforded  the  observer.  Figure  8s,  steep  spirals  and  banking  are  employed,  so 
the  observer  may  make  a  prolonged  observation  with  vision  unobstructed  by  wings, 
struts  or  other  parts  of  the  machine.  The  observer  is  charged  with  the  gathering  of 
facts;  opinions  and  deductions  may  be  made,  but  they  are  always  reported  as  such. 
Once  the  necessary  data  are  gathered  it  is  the  concern  of  both  pilot  and  observer  to 
bring  back  the  information  safely,  high  altitudes  being  sought  and  combat  avoided  by 
flight.  Hostile  aircraft  is  engaged  only  when  absolutely  necessary. 
PREPARATORY  RECONNAISSANCE 

Preparatory  reconnaissance  duty,  as  the  term  implies,  is  conducted  at  the  outbreak 
of  hostilities;  it  is  strategical  and  offensive  in  character.  The  objects  are  to  secure  all 
data  in  connection  with  the  enemy's  mobilization,  to  locate  depots  and  munition  bases 
and  plants,  to  harass  and  destroy  hostile  forces  by  air  raids,  interrupt  transportation 
and  break  lines  of  communication;  and,  up  to  the  point  of  concentration  and  establish- 
ment of  a  theatre  of  operations,  to  locate  all  hostile  forces  and  determine  their  strength 
and  mobility. 
TACTICAL  RECONNAISSANCE 

Observations  to  be  made  on  a  flight  order  for  a  tactical  reconnaissance  are  limited 
to  the  immediate  area  in  which  hostile  forces  are  in  contact.  A  two-seater  airplane 
with  radio  and  photographic  equipment  is  generally  used,  and  the  report  comprises 
detail  sketches,  the  positions  of  troops  and  fortified  terrain.  Reports  comprise  the 
following  information: 

Troops — Positions,  and  strength  of  reserve ;  movements,   enveloping  or  turning,  infantry  and   cavalry. 

Artillery — Positions   and  number  of  guns. 

Field  Trains1 — Positions  and  movements  of  combat  and  field  trains  behind  intrenched  positions. 

General — Evidences  of  strengthening  or  weakening  fortified  lines ;  activities  indicating  attack  in  force 
or  retreat. 

Tactical  reconnaissance  in  general  has  two  purposes  and  may  therefore  be  divided 
into  (a)  battle,  (b)  protective. 

Battle — Supplying  detailed  information  of  all  changes  and  developments  during 
the  course  of  action  by  which  the  commanding  general  may  estimate  the  situation  and 
form  decisions.  The  following  information  is  required:  Location  of  existing  and 
changing  trench  lines  and  batteries;  changes  in  tactical  disposition  and  distribution 
of  combat  troops;  arrival  and  departure  of  supporting  troops;  changes  in  location  of 
depots,  field  bases  and  lines  of  communication;  concealment  of  new  and  old  positions: 
movements  of  artillery,  new  positions,  number  and  calibers  of  guns;  movements  of 
transport  and  combat  wagons  and  trains. 

Protective — Information  similar  to  the  above,  but  relating  both  to  enemy  and 
friendly  forces,  is  secured  in  detail  during  a  retreat  of  friendly  forces.  The  command- 
ing general  by  this  means  is  enabled  to  keep  his  troops  under  full  control  and  estimate 
the  probable  moves  of  his  adversary. 

The  value  of  both  types  of  tactical  reconnaissance  lies  principally  in  the  continuity 
of  the  reports.  Airplanes  engaged  in  this  work  make  brief  but  regular  and  frequent 
observations,  working  in  relays  if  necessary.  From  captive  balloons,  in  rear  of  the 
actual  contact  of  forces,  supplementary  and  continuous  observation  is  made. 


Strategical  and  Tactical  Reconnaissance  173 

ESTIMATES  OF  ENEMY  STRENGTH 

Moving  Columns — Quick  computation  of  the  approximate  strength  of  columns 
moving  along  a  road  will  be  facilitated  by  the  following  rough  calculations: 

Infantry  in  column  of  squads  occupies  a  depth  of  about  l/2  yard  per  man,  a  column 
1  mile  long  contains  about  3,500  men. 

Cavalry  in  column;  of  fours,  about  1  yard  per  horse,  a  column  1  mile  long  containing 
about  1,500  troops. 

Artillery  in  single  file,  requires  about  20  yards  per  gun  or  caisson,  field  artillery 
having  about  50  guns  to  the  mile. 

Estimates  of  strength  may  also  be  roughly  calculated  by  the  time  taken  to  pass 
a  selected  point.  In  1  minute,  about  175  infantry  will  pass;  110  cavalry  at  a  walk,  200 
at  a  trot;  5  guns  or  caissons.  For  infantry  and  cavalry  in  column  of  twos,  take  one- 
half  of  these  figures. 

Confusion  of  combat  troops  with  transport  trains  and  artillery  should  be  guarded 
against.  Dust  clouds  will  help  the  identification,  if  the  troops  are  not  distinguishable, 
thus:  infantry  dust  clouds  hang  low;  cavalry  dust  clouds  are  higher  and  disperse  more 
quickly;  artillery  and  wagons  raise  dust  to  unequal  heights  and  of  disconnected  form. 

Reports  of  marching  columns  should  give  the  exact  location  of  the  troops  on  the 
map,  the  road  used,  direction  and  rate  of  march.  Gaps  in  the  column  and  unusual 
dispersions  should  be  noted  and  care  exercised  that  advance,  flank  and  rear  guards  are 
not  confused  with  the  main  body.  All  troops  on  foot  are  considered  combat  troops. 
Large  commands  are  accompanied  by  field  trains. 

Intrenched  Positions — Detailed  information  of  the  field  works  and  an  estimate  of  strength  with  the 
initial  deployment  of  troops  is  required. 

Trenches — By  photography,  sketches  and  notes,  complete  data  on  enemy  positions  are  secured.  The 
reconnaissance  establishes:  the  exact  line  of  field  works,  their  depth  including  reserves,  location  of  lines 
of  communication  and  field  headquarters.  Intrenchments  under  construction  are  reported  during  every 
stage  of  development  and  accurately  traced  and  located  during  and  after  erection  of  the  camouflage 
screen.  The  condition  of  enemy  barbed  wire  may  be  estimated  by  the  ground  smudges  and  spots, 
indicating  breaks  by  shell  fire. 

Combat  Troops — Estimates  of  strength  in  the  first  line  are  figured  as  one  man  per  yard.  In  initial 
deployments  the  strength  of  supports  and  reserves  is  of  greatest  importance,  as  two-thirds  of  the  force  of 
combat  troops  are  usually  held  in  the  rear. 

All  activities  should  be  noted,  including  changes  in  disposition  and  distribution  of  troops,  location  of 
flanks  and  movements  in  the  rear. 

Artillery — Battery  sites  should  be  located  and  all  changes  reported.  When  artillery  positions  are 
known  estimates  of  gun  calibers  may  be  made  by  the  range  bursts.  The  usual  maximum  for  field  artillery 
is  6,500  yards;  heavy  artillery  of  medium  caliber,  8,500  yards;  large  calibered  heavy  guns  and  howitzers 
have  ranges  ordinarily  beyond  the  scope  of  a  tactical  reconnaissance. 

STRATEGICAL  RECONNAISSANCE 

The  object  of  strategic  reconnaissance  is  to  prevent  surprise  by  the  enemy.  The 
term  is  applied  to  long  flights  over  wide  areas  and  to  considerable  depths  of  enemy 
territory,  observation  being  made  of  all  hostile  movements  and  developments  in  the 
theatre  of  war.  Airplane  squadrons  or  groups  with  large  radius  of  action  are  employed 
at  all  altitudes  from  1,000  to  12,000  feet.  Flights  for  information  of  strategic  importance 
should  be  so  frequent  as  to  be  almost  constant,  since  upon  the  information  thus  obtained 
the  commanding  general  must  base  his  plans  for  future  operations.  Photography  is 
extensively  employed,  but  notes  and  reports  are  less  concerned  with  details  than  with 
general  impressions  from  which  the  enemy's  intentions  may  be  calculated  or  deduced. 

Bases  and  Supply  Transport  activities  aid  in  disclosing  the  enemy's  intentions.  Railroads,  roads, 
rivers,  canals,  harbors,  depots,  airdromes,  lines  of  communication  and  bases  should  be  under  constant 
observation. 

Reconnaissance  over  wide  areas  is  of  greatest  value  when  reports  and  photographs  comprise  the 
details  given  below. 

Railroads — New  and  old,  direction,  number  of  tracks,  stations,  junctions  and  spurs ;  train  movements, 
size,  direction,  speed  and  frequency  of  travel. 

Roads — New   and   old,    nature,   condition,   intersection   with   railroads,   extent    and   character    of   traffic. 

Bridges — Position,    length    and    breadth,    materials    and    construction,    approaches    and    how    screened. 

Rivers  and  Canals — Direction,  width  and  depth,  rapidity  of  current ;  location,  size,  number  and 
direction  of  movement  of  vessels.  Number  and  location  of  locks  in  canals  and  islands  in  rivers. 

Villages  and  Towns — Their  situation  and  nature  of  the  surrounding  country ;  construction  and  type 
of  houses,  alignment  and  width  of  streets;  defenses. 

Woods — Situation,  extent  and  shape,  number  and  extent  of  clearings,  nature  of  roads  through  them, 
marshes  or  ravines  within;  whether  affording  cover  for  artillery  or  troops. 

Marshes — Extent  and  means  of  crossing,  defensive  measures  and  possible   uses. 
REPORTS   OF  FLIGHTS 

Reports  are  required  at  the  conclusion  of  all  flights,  whether  the  nature  of  the  mission  is  reconnais- 
sance, combat,  bombing,  or  special  duty.  These  are  preferably  presented  on  prepared  forms,  together  with 
maps,  sketches  and  notes.  Verbal  reports  may  be  made  if  the  need  is  urgent,  but  should  later  be  supple- 
mented with  a  detailed  written  report  at  the  earliest  possible  moment. 

The  observer  submits  reconnaissance  reports.  Serial  number,  time,  and  similar  data 
which  appeared  on  the  order  for  flight,  is  filled  in;  to  this  is  added  the  data  secured, 
arranged  in  chronological  form,  giving  the  exact  time  of  each  observation.  Special  remarks 
are  added  to  cover  air  combat  with  the  enemy  and  any  resultant  damage  to  the  airplane. 
The  course  followed  should  be  clearly  stated,  thus:  Cambrai — Denain — Valenciennes — 
Maubeuge — Aulnoye — le  Cateau — Cambrai. 


174 


Practical   Aviation 


Figure  142 — The  exactly  correct  method  of  gripping  the  telegraph  key 

A  B  C  D  E  F 


V 

•  ••I 


W 


PeViod 
••    •• 


4 

•  •••I 


9 

•  •• 


Understand 

Interrogation 
•  •«•«••• 

2 
6 

9 


Y 

Don't  Understand 


Exclamation 


•  ••I 


Call 


Finish 


Figure  143 — T/^^  General  Service  Code  of  the  U.  S.  Army,  variously  known  as  International, 

Continental  and  Wireless  Morse 


(C)  Comm.  Pub.  Info. 

U.  S.  Army  student  aviators  at  a  code  practice  table  used  for  instruction 


Signaling  Code  and  Method  of  Learning  175 

INSTRUCTION  IN  CODE  TELEGRAPHING 

Military  aviators  are  required  to  attain  a  fair  proficiency  in  code  telegraphy,  requir- 
ing about  40  hours'  study  on  the  average.  Application  of  the  dot  and  dash  method  of 
signaling  to  various  forms  of  electrical  and  visual  devices  largely  governs  communica- 
tion in  the  air  service  and  must  be  mastered.  The  following  text  will  prove  of  great 
assistance  in  learning  code  if  intelligently  used  by  the  student. 

THE  CODE 

Although  use  of  printed  code  charts  which  visualize  the  alphabet  is  generally  for- 
bidden the  beginner,  experience  has  proven  that,  deprived  of  these,  the  novice  will 
acquire  them  somehow,  so  the  General  Service  Code  of  the  U.  S.  Army  is  illustrated  in 
Figure  143.  This  alphabet  is  variously  known  as  International  Morse,  Continental 
Morse  and  the  Wireless  Code.  It  differs  from  American  Morse  principally  in  the 
elimination  of  the  spacing  between  symbols  making  up  a  letter. 

MEMORIZING  THE  CODE  / 

The  primary  rule  for  success  in  telegraphing  is  that  the  letters  must  be  learned 
by  their  sound.  Under  no  circumstances  is  the  student  to  attempt  to  visualize  each 
letter  by  dots  and  dashes.  An  excellent  method  for  those  who  feel  the  chart  essential 
in  the  early  stages  is  to  pronounce  the  syllable  "tub"  for  the  initial  dot,  "duh"  for  the 
other  dots,  and  "dah"  for  the  dashes,  the  letter  L,  for  example,  being  "tuh  dah  duh  duh." 
By  short  periods  of  practice  a  sense  of  the  rhythm  of  the  letters  is  thus  acquired.  Divi- 
sion of  the  chart  into  progressive  relationship  of  dots  and  dashes  has  also  proved 
convenient,  thus: 

E   .  T   _  A    .  __  A    .  M  N    mm 

I..  M_M  U..M  W.__  D_.. 

H  1 '. '. .  CH"ZJTinL  _  B  """ " " " 

R.  — .  N_.  ¥.„..__  N_. 

The  rule  governing  length  of  symbols  is:  Dash  is  three  times  as  long  as  dot. 
Space  between  letters  equals  duration  of  one  dot. 

PROPER  GRIP  ON  THE  KEY 

Figure    142   illustrates   the   exactly   correct  manner   of  holding   the  key.      The   positions   of  the   fingers 

are   relatively  the  same  as  for  holding  a  pen  or  pencil  with  a  diameter  as  large  as  the  key  knob thumb 

against  side  of  knob  to  steady  it;  index  finger  convexed  or  straight — never  concaved — and  second  finger 
resting  easily  in  position  over  the  key  knob.  The  wrist  should  be  relaxed  and  an  even,  light  pressure 
given  the  key.  Tapping  should  be  avoided.  Acquiring  the  correct  position  for  telegraphing  is  a  matter 
of  importance  for  the  novice,  as  clearness  in  forming  dots  and  dashes  is  largely  dependent  on  the  action 
of  hand  and  wrist. 
SENDING 

Some  instructors  have  stated  it  inadvisable  for  the  student  to  take  up  key  manipulation  before  pro- 
ficiency in  receiving  has  been  acquired.  Experience  dictates  that  sending  and  receiving  should  be  taught 
together,  for  the  student  in  early  training  invariably  receives  easiest  those  letters  which  he  sends  best. 

In  sending,  dots  should  be  made  short  and  sharp,  but  firm.  The  dash  is  made  three  times  as  long  as 
the  dot — but  not  by  pressure  three  times  as  hard.  Spaces  between  letters  are  the  duration  of  a  dot.  In 
forming  letters,  combination  of  dots  and  dashes  should  be  sufficiently  close  in  succession,  so  the  receiver 
cannot  mistake  the  combination  for  a  somewhat  similar  letter. 

Speed  above  10  or  12  words  per  minute  is  not  required  of  the  military  aviator,  but  absolute  accuracy 
is  insisted  upon.  Not  only  must  letters  and  numerals  be  formed  perfectly  but  spacing  of  groups  be  equally 
accurate.  Concentration  on  typical  signals  from  an  airplane  is  advisable,  for  learning  all  other  phases  is 
lost  time  from  the  military  aviator's  standpoint.  Examples  follow  : 

YWSF7  N4SL2  AC6E9 

and  so  on,  in  various  S-letter  arrangements  including  numerals.  A  considerable  number  of  abbreviations 
and  conventional  signs  are  ordinarily  appended  to  the  code  charts ;  all  of  these  need  not  be  memorized  by 
the  aviator,  the  following  being  sufficient : 

break  —  ...  —  correction 

end  of  message  .  —  .  —  .  ch 

RECEIVING 

The  signals  of  radio  (wireless)  and  buzzer,  with  which  the  airman  is  concerned,  are  exactly  counter- 
feited by  a  little  instrviment  known  as  a  practice  buzzer.  Where  the  candidate  wishes  to  prepare  himself 

before  going  to  the  army  schools — where  these  signals  are  received  in  head  telephones  at  practice  tables 

the  practice  sets  may  be  used  at  home,  or  the  Marconi-Victor  special  set  of  progressive  lesson  records  be 
listened  to  on  a  phonograph.  Receiving  practice  is  most  beneficial  when  students  are  paired,  alternately 
sending  to  each  other  for  15  minute  periods,  the  faults  of  one  thus  being  corrected  by  the  other  In  writing 
messages,  zero  is  distinguished  from  the  letter  O  by  placing  a  dot  in  its  center;  the  figure  1  is  made  with 
a  single  upstroke  so  as  not  to  be  confused  with  I.  The  entire  art  of  receiving  rests  on  the  one  orinciole 
emphasized  above— read  by  SOUND. 
VISUAL  SIGNALING 

The  average  time  devoted  to  an  aviator's  buzzer  instruction  is  34  hours;  6  hours  on  lamp  and  panneau 
(signaling  panel)   follows,  proficiency  in  visual  code  work  being  adequate  at  4  words  per  minute. 
PROFICIENCY  REQUIRED 

The  final  examination  for  aviators  determines  the  ability  to  send  and  receive  5-letter  words  at  a  speed 
of  8  words  per  minute  for  two  successive  minutes.  If  more  than  6  symbols  are  received  incorrectly,  or 
more  than  5  sending  mistakes  are  made,  the  applicant  has  failed  in  the  test.  In  sending,  an  interval 
omitted  or  misplaced  is  an  error. 


Practical    Aviation 


Com.  Pub.  Inf. 

The  air  service  cadets  in  the  gallery  are  simulating  all  the  conditions  of  an  aerial  observer  looking   down 

from  a  Plane  6  000  feet  high,  on  a  part  of  a  typical  earth  view  reproduced  in  the  map  below.     The  instructor 

in  the  lower  forefront  is  flashing  various  colored  lights,  representing  various  kinds  of  artillery  fire 


Methods  Used  in  Fire  Spotting  177 

DIRECTING  ARTILLERY   FIRE 

Regulation  of  artillery  fire  by  observers  in  airplanes  is  now  considered 
indispensable  in  warfare,  aerial  fire  correction  having  practically  superseded 
all  other  methods.  Fire  spotting,  while  distinct  in  many  ways  from  the  scout- 
ing duties  of  reconnaissance,  is  closely  related  to  tactical  operations  and  is 
therefore  included  under  the  broad  classification. 

Since  the  airplane  observer,  by  S-turn  and  circle,  hovers  over  the  target,  a 
comparatively  low-speed  machine  is  preferred ;  it  is  generally  a  two-seater, 
carrying  pilot  and  observer.  Wireless,  or  radio  telegraphy,  is  the  principal 
means  of  communicating  the  correction  for  the  artillery  and  has  almost  entirely 
replaced  former  means,  such  as  lamps  and  smoke  bombs.  Observers  for  artil- 
lery usually  work  in  two-hour  tours,  twice  a  day,  observations  being  made 
at  6,000  to  7,000-foot  altitudes.  They  are  required  to  know  something  of  types 
of  artillery,  shells  and  their  trajectories,  be  able  to  distinguish  distances  and 
characters  of  shell  bursts  by  the  smoke  puffs  and,  of  course,  understand  the 
manipulation  of  radio  transmitting  apparatus. 

METHOD  OF  TRAINING 

The  photograph  on  the  facing  page  clearly  shows  how  artillery  fire  spotting  is 
taught  The  student  observers  are  seated  in  a  gallery  looking  down  on  a  relief  painting 
which  visualizes  a  sector  of  the  earth  as  it  appears  at  an  elevation  of  6,000  feet.  By 
a  switchboard,  the  instructor  flashes  various  colored  lights,  representing  various  shell 
bursts;  these  blink  successively  at  numerous  points  on  the  miniature  battlefield,  for 
the  entire  area  is  wired  with  small  electric  lamps.  The  students  locate  the  flashes  on 
their  maps  and  record  the  required  signals,  the  simulated  artillery  fire  being  varied 
in  speed  by  the  instructor's  stop  watch. 

TYPES  OF  SHELLS 

Artillery  shells  are  (a)  common,  (b)  high  explosive,  (c)  shrapnel.  High 
explosive  shells  produce  black  smoke  when  they  detonate,  and  greenish-white 
smoke  otherwise.  Shrapnel  gives  off  a  white  smoke  pattern,  easily  seen  when 
the  shell  bursts  in  the  air,  but  difficult  to  observe  when  the  shell  is  exploded 
by  contact  with  the  ground.  Both  time  and  percussion  shells  are  used.  The 
degree  of  accuracy  required  in  striking  the  target  is  greater  with  the  high 
explosive  shell,  as  its  effect  is  limited  to  less  than  10  yards,  although  causing 
very  great  damage  within  that  area.  Shrapnel,  on  the  other  hand,  is  most 
effective  when  it  bursts  above  the  ground ;  when  time  fuses  are  used  the  shells 
explode  in  the  air  about  25  to  75  yards  short  of  the  target. 

RANGING 

The  observer  is  told  before  leaving  the  ground  whether  the  correction  to 
be  made  is  for  a  single  gun  or  an  entire  battery,  whether  the  fire  is  to  register 
positions  or  for  destruction,  and  whether  correction  is  to  be  given  for  line 
(right  and  left)  range  (over  and  short)  and  fuse  (burst)  or  all  three,  and  in 
what  order. 

One  of  the  principal  objects  of  the  flight  is  the  disclosure  of  new  enemy  batteries 
and  the  location  of  screened  or  camouflaged  positions.  When  the  target  has  been 
determined  and  shelling  begun,  the  result  of  the  fire  is  reported  by  wireless  by  a  pre- 
arranged code.  These  codes  vary  in  detail  and  are  changed  from  time  to  time  to  main- 
tain secrecy,  but  all  forms  require  use  of  small  divisions  of  the  military  map. 

OBSERVER'S  MAP  AND  CODE  SIGNALS 

The  map  of  the  sector  which  is  carried  by  the  observer  corresponds  exactly  with 
the  one  to  be  used  by  the  artillery.  It  is  usually  on  a  large  scale,  say,  3  inches  to  the 
mile.  Divisions  into  squares  are  made  so  that  smallest  squares  cover  a  very  small  area 
of  ground,  enabling  corrections  to  be  made  with  amazing  accuracy.  How  the  map  is 
divided  may  be  understood  by  careful  reading  of  the  following  explanation,  which  con- 
siders the  map  in  an  initial  division  into  squares,  and  three  subdivisions  into  progres- 
sively smaller  squares. 


178  Practical    Aviation 


Division — The  map  is  divided  into  24  equal  squares,  in  4  horizontal  rows,  6  squares 
to  a  row.  Each  section  is  marked,  progressively  from  left  to  right,  with  a  letter  of  the 
alphabet.  These  letters  are  Capitals,  A  to  X  inclusive. 

1st  Subdivision — Each  of  these  lettered  squares  is  subdivided  into  smaller  squares, 
the  top  row  (A  to  F)  and  the  bottom,  row  (S  to  X)  having  30  sections,  or  30  small  squares; 
the  two  inside  rows  (G  to  R  inclusive)  are  subdivided  into  36  small  squares 
each.  These  small  squares  are  given  a  number,  1  to  30  for  those  in  the  top  and  bottom  rows, 
1  to  36  for  those  in  the  inside  rows.  Thus  the  original  square  A,  for  example,  is  now  divided 
into  30  sections,  numbered,  left  to  right,  fom  1  to  30.  Squares  in  the  inside  rows,  G,  for 
example,  are  divided  into  36  numbered  squares;  1  to  36  inclusive.  The  map  which  was  first 
divided  into  24  squares  (A  to  X)  now,  therefore,  has  a  total  of  792  divisions. 

2nd  Subdivision — Each  of  these  792  small  squares  is  divided  into  4  parts,  lettered 
a,  b,  c,  d.  The  map  consequently  shows  a  division  thus  far  into  3,168  small  squares. 

3rd  Subdivision — Each  of  the  3,168  lettered  squares  (marked  a,  b,  c,  d,)  is  further 
divided  into  24  equal  sections,  these  still  smaller  squares  being  each  given  a  number  from 
1  to  24.  The  total  division  of  the  map  is  thus  seen  to  be  into  76,032  squares,  each  of  which 
represents  a  very  small  ground  area. 

The  signaling  is  simple.  A  shot  is  fired  and  the  point  where  it  strikes  is  located  on 
the  map  by  the  observer.  He  finds  it  has  landed  in  the  division  A,  in  its  lower  right  hand 
corner ;  say,  square  30.  This  square  being  divided  into  4  sections,  he  notes  that  the  shell 
has  struck  in  the  second  square  b,  and  since  the  exact  location  of  its  striking  point  there  is 
in  the  upper  left  hand  corner,  he  notes  the  designation  of  that  particular  square,  the 
numeral  1.  He  flashes  by  radio  to  the  artillery,  therefore,  the  following  message:  A-36-b-l. 
From  this  message  the  artillery  man  can  locate  the  point  where  his  shell  struck  with  almost 
minute  accuracy.  For  if  the  observer's  sector  comprises  as  much  as  6  square  miles,  he 
has  given  the  location  within  a  section  of  about  9  yards  dimension. 

A  high  explosive  shell  or  a  shrapnel  shell  dropping  within  this  distance  of  the 
target  will  have  the  desired  destructive  effect.  It  follows,  of  course,  that  if  the  area 
of  the  sector  under  observation  is  reduced  and  the  scale  increased,  the  location  can  be 
determined  to  pin-point  exactness. 

Owing  to  the  comparatively  small  size  of  the  page  in  this  book,  it  is  not  practical 
to  illustrate  the  division  of  the  map  by  a  diagram,  but  the  student  may  easily  visualize 
the  map  division  into  squares  by  laying  one  off  on  a  large  sheet,  and  following  the 
description. 

Another  method  of  signaling  the  results  of  shots  fired  at  a  definite  target  is  known 
as  the  clock  system.  By  this  method  the  point  where  the  shell  strikes  is  communicated 
relative  to  the  target.  Only  one  letter  and  one  numeral  are  required. 

The  dial  of  a  clock  is  divided  into  points  of  the  compass:  12  being  north;  6 
being  south;  9,  west;  and  3,  east.  The  target  is  the  center  of  the  dial.  From  this  center 
equally  spaced  circles  radiate  outward.  These  circles  represent,  say,  10  yard  intervals; 
they  are  progressively  lettered,  A,  B,  C,  Dt  etc.  Thus  the  signal  3-C  would  mean  that 
the  shell  struck  30  yards  east  of  the  target.  For  3  is  east  on  the  clock  dial  and  C  being 
the  letter  of  the  third  circle  from  the  center,  and  each  circle  being  spaced  10  yards 
apart,  3x10=30  yards. 

This  system  is  susceptible  of  almost  innumerable  changes,  as  the  relative  compass 
positions  merely  have  to  be  shifted  to  other  numerals  on  the  clock  dial,  and  the  interval 
between  circles  be  given  a  different  value  in  yards  or  feet. 

As  more  than  one  observer  may  be  using  the  clock  system  at  the  same  time  in 
nearby  localities,  each  battery  has  a  code  symbol,  frequently  changed,  which  the 
observer  calls  before  sending  his  fire  correction. 

SIGNALS  FROM  THE  GROUND 

When  fire  is  centered  on  a  target  or  the  objective  destroyed  the  aviator  is  given 
a  new  position  by  signals  from  the  ground.  These  are  generally  of  visual  character, 
although  the  remarkable  development  of  radio  promises  wireless  reception  by  the 
airman  in  the  near  future. 

The  usual  means  employed  for  visual  communication  are  shutter  panels,  lanterns 
or  heliograph  mirrors;  by  these,  lettered  abbreviations  are  signaled  in  telegraph  code; 
or  3  white  canvas  strips  measuring  15x3  feet  are  laid  on  the  ground  to  form  various 
characters  with  predetermined  meanings.  Thus  X  might  mean  "Commence  observing 
for  range";  V,  "Go  out";  I,  "Come  in";  N,  "Cannot  comply  with  last  signal"  or  "Dis- 
tress"; T,  "Turn";  H,  "Incline  to  the  right";  L,  "To  the  left";  II,  "Descend";  III,  "Ob- 
serve for  burst,"  etc.,  etc.  These  meanings  and  arrangements  of  the  3  strips  are  obvi- 
ously easy  of  variation  to  maintain  secrecy. 

Radio  messages  should  not  be  sent  while  the  airplane  is  turning. 
Sending  with  the  machine  pointed  toward  the  ground  station  facilitates 
easy  reception. 


Theory  of  Wireless  Telegraphy  179 


RADIO  (WIRELESS)  TELEGRAPHY 

Extensive  knowledge  of  radio,  or  wireless  telegraph  sets  is  not  required  of  the 
military  aviator,  except  for  those  who  specialize  in  this  art,  in  which  case  full  knowl- 
edge of  theory  and  practice  is  essential.*  All  aviators,  however,  in  addition  to  skill  in 
code  sending,  must  have  some  knowledge  of  the  parts  and  connections  of  the  apparatus. 
An  outline  of  the  theory  of  radio  and  a  brief  description  of  a  typical  airplane  wireless 
set  will  therefore  comprise  the  limited  discussion  here. 
THEORY  OF  RADIO  TRANSMISSION 

A  radio  sending  set  comprises  an  assembly  of  electrical  devices  which  generate 
and  control  an  electrical  wave  motion,  so  that  when  the  circuit  is  interrupted  disturb- 
ances are  created  in  the  ether  in  the  air,  of  long  and  short  (dot  and  dash)  duration. 
These  disturbances,  or  waves,  may  be  compared  to  the  radiating  ripples  caused  by  a 
stone  dropping  into  water,  excepting  that  they  travel  in  the  ether  with  the  speed  of 
light,  186,000  miles  per  second.  Reception  of  signals  is  possible  only  through  properly 
attuned  electrical  apparatus;  viz.,  the  radio  receiving  set.  Thus  radio  transmission 
might  be  further  comparable  to  the  voice,  as  a  transmitter,  sending  vibrations  of  vary- 
ing intensity  in  waves  through  the  air,  registering  only  on  attuned  ears,  the  receiver. 

Easiest  understanding  of  the  apparatus  which  comprises  a  radio  transmitting  set  is 
gained  by  classifying  according  to  their  functions  in  utilizing  electrical  energy,  the  re- 
spective missions  being:  (a)  generation,  (b)  regulation,  (c)  transformation,  (d)  control. 

He-fore  considering  these  in  classification  and  in  their  relation  to  each  other,  a  few  electrical  defin '.- 
lions  are  necessary. 

VOLT — The   unit  of  pressure,   or  electromotive  force. 

AMPERE- — The  unit  of  current  flow,  comparable  to  gallons  of  water  flowing  through  a  pipe,  or 
revolutions  of  an  engine,  per  second. 

KILOWATT  (Kw.)—  The  unit  giving  the  power  required  for  specified  work  in  a  given  time  (Kw.= 
volts  4-  amperes). 

DYNAMO — A  mechanically  driven  machine  which  rotates  a  wire  coil  within  a  magnet,  the  resulting 
induced  current,  or  electromotive  force,  being  collected  by  brushes. 

DIRECT    CURRENT    (D.C.) — An   electrical   current   constant   in    direction. 

ALTERNATING  CURRENT  (A.C) — A  current  changing  rapidly  back  and  forth  from  positive  to 
negative  direction. 

OPERATIONS  IN  THE  CIRCUITS 

Tracing  the  current  through  its  successive  movements  in  the  airplane  radio  trans- 
mitting set  is  made  easier  by  classification  of  apparatus  into  four  divisions  by  function : 

GENERATION — A  small  air  screw,  placed  at  the  front  of  the  airplane  and  rotated  by  the  wind  when 
the  craft  is  flying,  supplies  the  mechanical  force  which  drives  the  dynamo.  Direct  current  (D.C.)  is  thus 
produced.  But  direct  current  cannot  be  transformed  to  the  high  voltages  (pressure,  or  electromotive 
force)  necessary  to  transmit  the  radio  signals  through  space,  so  alternating  current  (A.C.)  is  produced  in 
a  special  dynamo,  or  alternator. 

Both  D.C.  and  A.C.  dynamos  are  usually  contained  in  the  same  pear-shaped  case,  the  D.C.  current 
being  required  to  excite  the  coils  of  the  A.C.  dynamo,  or  alternator.  The  combined  apparatus  is  known 
as  a  separately  excited  alternator. 

Sets  used  on  training  planes  often  have  storage  batteries  in  place  of  the  D.C.   dynamo. 

REGULATION — A  coil  of  wire,  known  as  a  resistance  coil,  or  field  resistance,  allows  the  power  out- 
put of  the  alternator  to  be  varied  by  setting  sliding  contacts  so  as  to  include  many  or  few  turns  of 
resistance  wire. 

TRANSFORMATION — The  amount  of  alternating  current  selected  then  goes  to  the  transformer, 
where  the  low  voltage  is  converted  into  high  voltage  A.C. 

The  high  voltage  current  then  feeds  to  the  condenser,  where  the  electrical  energy  is  stored  up  in  the 
spaces  between  plates  made  of  copper  or  some  i  conducting  material.  This  current  discharges  periodically 
(usually  1,000  times  per  second)  through  the  oscillation  transformer  and  across  the  spark  gap. 

The  oscillation  transformer  regulates  the  condenser  discharges  of  the  current  to  frequency  desired, 
by  variation  of  the  number  of  turns  of  copper  ribbon  of  which  it  is  composed. 

The  spark  gap  acts  as  a  valve,  discharging1  the  condenser  when  the  telegraph  key  is  depressed,  caus- 
ing an  electrical  spark  to  jump  across  the  gap  between  its  two  terminals. 

When,  by  pressing  the  telegraph  key,  the  flow  of  current  through  the  circuit  of  the  spark  gap  is 
interrupted,  the  current  goes  to  the  aerial  or  antenna  (a  wire  trailing  from  the  airplane),  and  part  of  its 
energy  is  radiated  into  space  in  the  form  of  electro-magnetic  waves.  These  electrical  displacements  are 
long  and  short  according  to  the  sequence  of  dashes  and  dots  made  by  the  key. 

CONTROL — It  is  obvious  that  without  means  provided  for  regulating  the  length  of  the  radiated 
wave,  there  would  be  conflict  between  a  number  of  wireless  messages  hurtling  through  space,  the  dotsj 
and  dashes  would  be  confused  and  could  not  be  understood.  Therefore,  radio  sets  send  their  signals  out 
in  selected,  definitely  measured,  WAVE  LENGTHS. 

The  control  devices  used  for  this  purpose  are :  the  oscillation  transformer,  already  referred  to,  the 
aerial  tuning  coils  and  the  variometer.  The  aerial  tuning  coils,  by  increasing  or  reducing  the  number  of 
turns  of  wire  placed  in  the  aerial  circuit,  lengthen  or  shorten  the  radiated  wave.  The  variometer  (con- 
sisting of  two  coils  opposed  to  each  other)  permits  a  finer  adjustment  of  wave  length  than  the  aerial  coils 
alone  could  give. 

Wave  lengths  are  measured  in  meters.     Placing  a  wave  length  changing  switch  to  the  desired  numeral 
on   a  dial   sets   the   control   devices    for   the   operator.      An    aerial   ammeter,    by    its   needle   indicator,    shows 
whether   the   flow   of   electrical   energy   is   at   maximum   for   the   radio   set's   best   operating   efficiency. 
RADIO   RECEIVERS 

Description  of  the  construction  and  operation  of  radio  receiving  sets  will  not  be  included  here,  as 
at  present  the  military  aviator  is  not  concerned  with  their  manipulation.  The  day  is  not  far  distant, 
however,  when  wireless  telegraphy  and  telephony  will  take  the  place  of  visual  communication  to  aircraft, 
and  for  those  who  wish  to  specialize  in  radio,  time  will  be  well  spent  in  study  of  receiving  apparatus. 
Space  limitations  do  not  permit  discussion  of  receivers  here,  but  excellent  textbooks  which  go  exhaus- 
tively into  the  subject,  may  be  secured  at  low  cost. 

*  Practical   Wireless   Telegraphy,   by   Bucher,   is   the   most  suitable   textbook,   in   the   Author's   opinLn. 


180 


Practical    Aviation 


Figure  144—View  of  the  interior  of  a  typical 
airplane  radio  transmitter 


Figure   145 — Diagram   of   the   circuits  of   the 
radio  transmitting  set  shown  above 


AIRPLANE  RADIO  APPARATUS 

Great  advances  have  been  made  in  the  design  of  radio  apparatus  for  airplanes,  and 
sets  remarkable  both  for  mechanical  and  electrical  perfection  are  now  in  use  in  war- 
fare. For  military  reasons,  these  cannot  now  be  described.  The  aviator,  being  con- 
cerned with  knowledge  of  fundamentals  only,  may  acquire  these  from  the  transmitting 
set  pictured  in  photograph  and  diagram  on  this  page.  It  is  of  enemy  manufacture,  and 
a  fair  specimen  of  short-range  radio  apparatus  used  on  military  airplanes. 

The  generator  is  not  shown,  as  it  is  of  the  usual  type,  but  the  photograph  of  the  set's  interior,  Figuro 
144,  clearly  identifies  the  various  parts  of  the  sending  apparatus.  The  diagram  of  connections,  Figure  145, 
is  arranged  for  easy  reference,  the  course  of  the  electrical  current,  as  given  in  the  description  following, 
being  in  a  general  direction  from  right  to  left. 


Description  of  An  Airplane  Wireless  Transmitter  181 

The  classification  scheme,  outlined  on  page  179,  is  applied  to  the  apparatus  as 
follows: 

GENERATING  THE  ELECTRICAL  POWER 

Referring  to  the  lower  right  of  the  diagram,  the  exciter  (a  small  generator)  furnishes  initial  current 
to  the  field  magnets  of  the  D.C.  dynamo;  the  latter  in  turn  supplies  field  current  required  by  the  alternator 
(A.C.).  All  of  these  comprise  the  generating  unit,  which  is  mechanically  driven  by  a  small  air  screw,  as 
explained  on  page  179.  The  current  is  delivered  by  the  generator  at  pressures  from  110  to  500  volts, 
oscillating  at  150  to  500  cycles  per  second. 

REGULATING  THE  POWER  OUTPUT 

Regulation  of  the  generator's  output  (110  to  500  volts)  is  secured  by  the  field  resistance  coil  (upper 
right  of  diagram).  This  generator  control  circuit  is  indicated  by  the  broken  lines. 

TRANSFORMING   THE    ENERGY 

The  alternating  current  flowing  from  the  generator  (A.C.)  enters  the  transformer  (center  of 
diagram)  by  the  primary  coil  (P).  This  cpil  consists  of  a  few  turns  of  coarse  wire  wound  about  an 
iron  core.  The  core  also  has  a  second  winding  of  finer  wire  and  greater  number  of  turns,  known  as  the 
secondary  (S).  The  current  surging  through  the  primary  (P)  "steps  up"  the  current  in  the  secondary 
(S)  to  10,000  to  15,000  volts,  the(  electromotive  force  necessary  for  this  particular  type  of  set  to  transmit 
radio  signals. 

This  high  voltage  current  then  enters  the  condenser,  where  it  is  stored  up  temporarily,  the  con- 
denser discharging  periodically  (as  explained  on  page  179)  through  the  oscillation  transformer  across 
the  spark  gap. 

When  the  telegraph  key  is  depressed,  the  alternating  current  (oscillating  at  high  frequency)  is  dis- 
charged from  the  condenser  across  the  spark  gap,  which  suddenly  quenches  out  the  current  flow  in  the! 
circuit,  including  the  condenser,  oscillation  transformer  and  the  spark  gap.  This  transfers  (by  electro- 
magnetic induction)  the  current  to  the  circuit,  oscillation  transformer-AERIAL.  The  energy  is  then 
radiated  from  the  aerial  into  space  as  an  electric  wave  motion.  Long  and  short  pressure  on  the  key 
thus  releases  the  energy  in  dashes  and  dots  of  the  code.  The  aerial  is  a  lightly  weighted  trailing  wire 
which  passes  through  the  floor  of  the  fuselage  and  is  unwound  to  the  required  length  from  a  reel  operated 
by  a  clutch. 

CONTROLLING  THE  LENGTH  OF  THE  RADIATED  WAVE 

It  has  been  explained  that  to  avoid  conflict  of  many  wireless  messages  in  the  air  at  the  same 
time,  the  electromagnetic  waves  are  measured  in  definite  wave  lengths.  The  radio  transmitting  set 
illustrated  is  designed  to  send  its  message  on  three  wave  lengths,  150  meters  or  200  meters  or  250 
meters.  This  means  that  the  operator  on  the  ground  who  is  to  receive  the  aviator's  wireless  message 
will  attune  his  set  to  one  of  these  waves,  selected  according  to  the  interference  prevailing  and  the  dis- 
tance to  be  spanned. 

Adjusting  the  various  parts  of  the  apparatus  so  the  radiated  wave  will  have  the  desired  length  is 
accomplished  by  setting  knobs  and  switches  on  the  top  of  the  transmitter  case.  It  is  the  principal 
adjustment  required  of  the  operator,  and  the  resultant  action  in  the  circuits  is  the  most  difficult  for 
the  student  to  understand. 

First  it  must  be  known  that  the  length  of  the  wave  radiated  from  the  aerial  has  direct  relation  to 
the  frequency  of  oscillation  of  the  current  flowing  in  it.  That  is :  wave  length  =  the  velocity  of 
electricity  -f-  the  frequency  of  the  currents  in  the  aerial.  Since  electricity  travels  at  300,000,000  meters 
per  second,  if  it  is  determined  that  the  current  in  the  aerial  is  oscillating  at  1,000,000  cycles  per  second, 
then  300,000,000  -f-  1,000,000  =  300  meters,  the  wave  length  radiated.  Since  the  set  illustrated  in  the 
photograph  is  designed  to  radiate  wave  lengths  of  150,  200  and  250  meters  it  is  seen  that  the  frequency 
of  oscillation  of  the  currents  in  the  aerial  must  be:  2,000,000  for  150  meters;  1,500,000  for  200  meters; 
1,200,000  for  250  meters. 

For  successful  operation  with  this  extremely  high  frequency  the  rate  of  current  oscillation  must  be 
the  same  in  the  certain  parts  of  the  apparatus  which  comprise  the  radio  set. 

Recalling  that  depressing  the  key  transfers  the  current  from  condenser  and  spark  gap  to  the  aerial, 
tv/o  natural  divisions  of  the  complete  circuit  are  evident,  viz : 

Closed   Circuit — Condenser-spark   gap-oscillation   transformer. 

Radiating   Circuit — Oscillation  transformer-aerial  tuning  coils-aerial  and  grounded   circuit. 

These  are  termed  the  radio  frequency  circuits  of  the  transmitter.  To  regulate  the  currents  in  these 
circuits  so  that  their  frequency  is  identical  in  both  is  the  principal  function  of  most  of  the  apparatus 
which  comprises  the  radio  set.  Adjustment  of  the  two  circuits  to  the  required  resonance  will  be  de- 
scribed : 

CLOSED  CIRCUIT 

The  operator  turns  the  knob  Power  Control  (seen  in  the  photograph,  Figure  144,  on  top  of  the 
cabinet  a  trifle  on  the  right  of  center).  This  simultaneously  controls  the  output  from  the  motor  gen- 
erator and  the  number  of  plates  of  the  spark  gap  to>  be  connected  in  the  circuit.  The  diagram,  Figure 
145,  shows  how  this  is  accomplished.  The  control  rod  when  turned  to  the  position  P-l  leaves  only  a 
tew  turns  of  wire  in  the  field  resistance  coil  to  oppose  the  current  from  the  exciter  of  the  alternator,  a 
larger  proportion  of  its  current  output  being  thus  obtained.  At  the  same  time  the  control  has  acted 
on  the  spark  gap,  cutting  in  most  of  its  plates.  When  the  control  switch  is  thrown  to  position 
P-2,  exactly  the  reverse  happens:  More  turns  in  the  resistance  coil  oppose  the  flow  of  current  from 
the  exciter,  and  less  plates  in  the  spark  gap  are  left  in  circuit.  The  balance  of  adjustment  for  the  closed 
circuit  is  made  by  the  wave  length  changing  switch  (center  top  of  cabinet  in  the  photograph)  which, 
as  shown  in  the  diagram,  cuts  in  a  fixed  number  of  turns  of  the  oscillation  transformer  when  the 
switch  is  set  to  the  selected  contacts  marked  for  150,  200  or  250  meters. 

RADIATING  CIRCUIT 

It  should  be  noted  that  the  oscillation  transformer  also  aids  the  adjustment  for  resonance  between  the 
closed  and  the  radiating  circuits.  The  diagram  shows  how  additional  closeness  of  adjustment  is  ob- 
tained in  this  circuit.  Trie  aerial  tuning  coils  L-l  and  L-2  and  L-3  connected  to  the  contacts  K-'l,  K-2 
and  K-3  add  the  necessary  turns  for  a  progressive  increase  in  wave  length  as  the  switch  is  moved  on 
the  contacts  from  150  to  200  or  250  meters.  The  fine  adjustment  for  complete  resonance  is  obtained  by 
the  variometer  coils,  L-4  and  L-5,  which,  when  placed  near  or  drawn  away  from  each  other,  have  the 
same  effect  as  cutting  in  or  out  turns  of  coils  L-l.  L-2  and  L-3.  When  the  set  is  put  into  operation, 
the  wave  length  desired  is  obtained  by  turning-  the  knob  controlling  the  aerial  tuning  coils  (in  the  photo- 
graph, top  left)  until  the  ammeter's  needle  gives  the  maximum  reading. 

To  the  novice,  wireless  telegraphy  and  the  apparatus  used  appears  heayely  technical.  But  a  large 
part  of  the  mystery  will  disappear  if  the  aviator  carefully  re-reads  the  outline  of  the  theory  contained 
on  this  page  and  page  179,  referring  constantly  to  the  diagram  and  bearing  in  mind  the  divisions  made  of 
the  apparatus  according  to  function. 


182 


Practical    Aviation 


(C)    Int.    I^ilm   Svce. 


This  remarkable  airplane  picture,  considered  by  the  military  experts  to  be  among  the  greatest  ever  taken, 
shows  one  of  the  biggest  concentration  camps  at  which  munitions  and  men  were  assembled  for  the  1918  spring 
drive  of  the  Germans.  Here  is  the  official  report  of  what  the  picture  shows: •  1— Supply  railway  trams  running 
on  newly  laid  tracks.  2— Piles  of  supplies,  chiefly  timbers  for  use  in  building  dugouts.  3—holls  of  barbed 
wire.  4— -Piles  of  iron  stakes  for  stringing  barbed  wire.  5— Steel  roofing  for  dugouts. 


Reconnaissance  Photo  of  Enemy  Base 


183 


6 — Site  of  railway  station.  Note  big  shell  craters  (about  sixty  feet  across)  caused  by  420  MM.  shells. 
7t  8,  9 — Remains  of  former  railway  tracks  where  they  entered  railway  station.  10 — Broken  ties  of  former 
railway  tracks.  11 — Other  supplies  piled  tip.  Perishable  goods  covered  over  with  tent  cloth.  12 — Battery  of 
•four  guns,  with  abris  for  gunners.  13 — Commander's  dugout.  14 — Ammunition  park.  Note  enemy  soldiers 
standing  around,  15 — German  soldiers  standing  in  the  road  watching  the  airplane. 


184  Practical    Aviation 

AERIAL  PHOTOGRAPHY 

Reconnaissance  photography  from  airplanes  is  a  tremendously  important  branch 
of  the  air  service.  Military  maps  upon  which  offensives  are  based  are  assembled  from 
prints  of  various  small  sections  of  the  theatre  of  operations,  disclosing  to  the  com- 
manding general  the  exact  location  of  all  enemy  batteries,  entrenchments  and  fortified 
positions,  lines  of  transport  and  communication.  By  constant  activity  the  camera  men 
keep  these  maps  accurate  up  to  within  a  few  hours.  Expertness  in  photography  re- 
quires considerable  study  and  practical  experience;  but  such  skill  is  required  only  of 
specialists.  Military  observers  and  pilots  are  ordinarily  required  merely  to  arrive  over 
the  objective  and  snap  the  camera's  shutter.  Some  knowledge  of  photographic  funda- 
mentals will  be  found  useful,  however. 

THE  CAMERA  AND  ITS  PARTS 

Camera — A  light  tight  box  with  a  lens  at  one  end  and  a  support  for  films  or  plates  at  the  other. 
By  means  of  a  shutter  objects  are  projected  through  the  lens  on  the  sensitive  film  for  fractional  inter- 
vals of  time.  Bellows,  for  folding  the  camera  to  smaller  dimensions  ;  stops,  for  regulating  the  projected 
rays,  and  various  other  attachments,  are  auxiliary  devices.  In  airplane  photography  there  are  two  main 
types  of  cameras,  (a)  automatic,  (b)  pistol.  The  automatic  camera  has  regulating  attachments  which, 
when  started,  automatically  make  a  series  of  consecutive  views  of  the  course  of  flight  over  the  selected 
locality.  By  means  of  a  guide  line  the  points  of  union  of  two  adjacent  views  is  indicated,  and  from 
the  focal  angle  of  the  lens  and  the  altitude  when  exposure  was  made,  a  scale  of  distances  is  computed. 
The  pistol  type  has  the  general  form  of  that  weapon  and  a  trigger-operated  shutter.  It  is  used  in  flight 
for  taking  close-up  photographs  of  enemy  airplanes,  from  which  construction  details  of  new  types  may 
be  secured.  For  training  in  aerial  gunnery  the  pistol  type  of  camera  is  also  useful,  being  mounted 
rigidly  on  the  plane  and  directed  at  other  machines  in  flight,  guide  lines  on  the  developed  picture  indi- 
cating the  accuracy  of  aiming. 

Finder — A  ground  glass  panel  which  indicates  the  limits  of  the  camera's  field  of  vision,  generally 
placed  at  the  rear  end  of  the  camera  or  between  and  below  the  aviator's  feet. 

Lens — Curved  and  transparent  glass  arranged  to  cause  the  luminous  rays  to  either  converge  or 
diverge  on  the  film  or  plate.  Lenses  are  (a)  single,  (b)  double,  (c)  anastigmat.  The  latter  have 
superiority  over  the  others  in  illuminating  and  converging  power  and  highest  correction. 

Stops  or  Diaphragm  Openings — The  device  which  regulates  the  converging  of  the  rays  of  light 
at  or  near  the  center  of  the  lens,  smaller  openings  cutting  off  other  rays  of  light  and  making  sharper 
and  clearer  images  on  the  picture.  Knowledge  of  the  correct  use  of  stops  is  essential  to  good  photog- 
raphy. 

Films  and  Plates — These  are  strips  of  celluloid  or  glass  plates  coated  with  a  film  of  salts  sensitive 
to  the  chemical  action  of  light.  The  emulsion  is  composed  of  salts  of  silver,  bromide  of  potassium  and 
gelatine.  After  exposure  to  the  light,  the  bromide  of  silver  is  changed  to  a  state  where  that  part  of 
the  coating  exposed,  when  placed  in  a  solution  known  as  developer,  takes  the  form  of  metallic  silver 
having  a  dark  color.  Introduction  of  a  fixing  solution  (hyposulphite  of  soda  and  water)  dissolves  all 
the  bromide  of  silver  excepting  the  dark  silver  salts  which  carry  the  image  of  the  object  revealed 
by  the  exposure.  This  image  appears  as  a  negative,  the  same  chemical  actions  transferring  its  dark 
portions  to  lighter  ones  on  the  photographic  print  paper. 

ARRANGEMENT  OF  CAMERAS 

In  airplane  photography  for  military  purposes  a  favored  arrangement  provides 
for  three  cameras  pointing  downward,  the  field  of  vision  of  each  ending  precisely 
where  its  predecessor  begins,  affording  a  panoramic  view  of  the  locality  photographed. 
The  control  is  automatic;  the  three  shutters  operate  by  a  push  button,  pressure  of  a 
lever  forward  then  removing  the  plates  from  the  cameras.  The  same  lever,  pulled 
back,  inserts  the  new  plates  and  makes  all  ready  for  the  next  exposure. 

PHOTOGRAPHIC    FLIGHTS 

Two  or  three  times  a  day  during  the  progress  of  hostilities,  reconnaissance  airplanes  fly  over  the 
enemy  territory  to  a  depth  of  10  to  15  miles,  being  engaged  in  photographic  work  sometimes  6  hours  per 
day.  Two  types  of  airplanes  are  used;  the  two-seater  with  a  speed  of  120  to  140  miles  per  hour, 
escorted  by  a  formation  of  fast  combat  machines,  and  the  single-seater,  which  goes  out  with  small  combat 
patrols  of  three  or  four  planes.  The  convoys  are  piloted  by  highly  trained  specialists  in  formation  flying 
and  air  tactics.  Prescribed  actions  for  each  machine  in  the  formation  are  executed  on  a  single  signal  to! 
meet  almost  any  form  of  attack;  all  of  these  evolutions  have  for  their  object  the  protection  of  the  photo- 
graphing airplane,  the  chief  duty  of  the  escort  being  to  shield  the  reconnaissance  machine  during  the 
entire  journey.  Photography  from  single-seaters  in  small  groups  is  of  a  scouting  nature,  to  keep  the 
maps  at  headquarters  .up  to  date. 

Military  information  contained  in  photographs  made  in  the  air  is  generally  superior  to  the  reports 
possible  when  only  the  naked  eye  is  employed.  Minute  details,  such  as  wagons  on  roads,  are  revealed  in 
exposures  made  at  12,000  to  15,000  feet.  Rain,  thick  mist  and  low-hanging  cloud  masses  present  con- 
ditions which  make  air  photography  usually  impossible,  but  certain  forms  of  mist  impenetrable  to  the 
eye  will  be  pierced  by  the  camera  lens.  Best  conditions  are  represented  by  clear  skies  or  high  cloud 
masses  which  reflect  the  light  down.  One  of  the  special  values  of  reconnaissance  photographs  is  in 
revealing  camouflage.  Twin  prints  placed  in  a  stereoscope  show  the  solid  objects  in  their  proper  per- 
spective, whereas  the  overhead  camouflage  cover  appears  flat. 
MAPPING  FROM  PHOTOGRAPHS. 

Immediately  upon  landing,  the  laboratory  men  dismount  the  cameras  or  secure  the  plates  or  films  and 
rush  with  them  to  nearby  developing  rooms  mounted  on  motor  trucks.  Within  15  minutes  the  negatives 
are  developed.  Without  waiting  for  prints,  the  negatives  are  placed  in  a  stereopticon  or  balopticon  lantern 
and  thrown  on  a  screen.  If  the  magnified  view  discloses  a  new  enemy  position,  its  location  is  quickly 
given  to  the  artillery  commander.  Prints  meanwhile  are  rushed  to  headquarters  where  a  group  of  experts' 
reduce  them  to  scale,  determine  the  overlapping  lines  and  paste  them  together  to  form  a  photographic 
map.  These  maps  show  every  detail  of  the  enemv  terrain  and  skilled  artillery  observers  with  magnifying 
glasses  search  them  for  all  indications  of  new  military  works  of  importance.  Scouting  trips  provide  the 
pictures  which  keep  the  map  continuously  correct  to  within  a  few  hours. 

The  wide  area  which  may  be  mapped  by  airplane  photography  may  be  appreciated  by  consideration 
of  the  field  of  vision  of  a  camera.  This  is  determined  by  the  altitude,  an  8-inch  lens  at  a  height  of 
10,000  feet,  for  example,  having  a  field  of  more  than  a  square  mile. 


Practical    Aviation  185 


REVIEW    QUIZ 

Reconnaissance  and  Fire  Spotting 

1.  What  preparations  are  required  of  pilot  and  observer  immediately 

upon  receipt  of  orders  for  a  reconnaissance  flight? 

2.  State   the   difference   between  a   strategical  and   a   tactical   recon- 

naissance. 

3.  About  how  many  men  will  be  in  a  column  of  infantry  a  mile  long, 

marching  in  column  of  squads?  Cavalry,  in  column  of  fours? 
How  many  of  the  infantry  will  pass  a  selected  point  in  one 
minute?  How  many  of  the  cavalry? 

4.  State  in  detail  the  data  required  by  the  various  headings  of  a  recon- 

naissance report. 

5.  Explain  what  is  meant,  in  ranging  for  artillery,  by  the  corrections 

for  line,  range  and  fuse. 

6.  How  are  observers'  maps  divided  for  location  of  objectives  and  why 

are  both  letters  and  numerals  used? 

7.  Describe  the  clock  system  of  reporting  shell  hits. 

8.  Give   the  direction  of  airplane  flight  which  is  most  favorable  for 

sending  radio  signals.  During  what  airplane  movement  should 
they  be  suspended? 

9.  How  must  the  letters  of  the  telegraph  code  be  learned? 

10.  What  is  the  proper  position  of  the  hand  on  the  key? 

11.  Give  the  rule  which  governs  the  lengths  of  the  dot  and  the  dash. 

12.  Give   the    abbreviations    for    "break,"    "correction,"    "ch,"    "end   of 

message." 

13.  Explain  how  the  image  is  registered  on  a  photographic  film  or  plate. 

14.  State  the  atmospheric  conditions  favorable  and  unfavorable  to  aerial 

photography. 

15.  How  are  photographs  employed  to  disclose  camouflage? 

16.  Classify  the  parts  of  a  radio  set  into  four  divisions  by  function. 

17.  Why  must  the  high  frequency  current  be  regulated  so  the  radiated 

wave  will  have  a  definite  wave  length? 

18.  For  generation  of  current  for  the  airplane  radio  set  described,  why 

are  both  D.  C.  dynamo  and  A.  C.  dynamo  required? 

19.  What  is  the  difference  between  a  closed  circuit  and  a  radiating  cir- 

cuit? 

20.  What  is  meant  by  resonance  between  these  two  circuits  and  which 

parts  of  the  apparatus  establish  it? 


186 


Practical    Aviation 


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APPENDIX 

Nomenclature  for  Aeronautics 
With  the  French  Equivalents  and  Phonetics 

The  following  glossary  of  terms  will  serve  as  a  guide  to  the  new  and  peculiar  language  of 
aeronautics.  The  definitions  are  largely  taken  from  those  prepared  by  the  National  Advisory  Com- 
mittee for  Aeronautics. 

The  French  equivalents  and  phonetics  for  pronunciation  have  been  checked  by  French  aviators. 
No  key  is  needed  ;  where  it  has  been  possible  to  give  the  sound  by  a  short  word  or  syllable,  such 
as  "day,"  it  is  so  given.  Perfection  in  phonetics  is  impossible  of  achievement,  for  the  reason  that 
there  are  sounds  in  French  which  have  no  equivalent  in  English.  But  if  the  words  are  spoken  as 
they  read,  no  difficulty  will  be  experienced  in  being  understood.  Where  the  small  r  and  ng  appears 
above  the  line,  it  indicates  that  the  reader  prepares  to  sound  the  word  or  syllable  -with  the  r  or  ny 
included,  but  cuts  off  the  r  or  ng  before  it  is  actually  spoken.  This  gives  the  peculiar  sound  to  French 
words  which  is  erroneously  termed  nasal.  Those  who  speak  English  will  have  principal  difficulty 

S~+*  X-N  S~** 

in  pronouncing  syllables  which  are  here  given  phonetically  as  eur,  deu,  pen.  The  exact  sound  is 
difficult  of  accomplishment  without  practice  to  develop  the  vocal  chords.  But  it  can  be  mastered  to 
entire  satisfaction  if  the  lips  are  pursed  as  for  whistling  and  held  firmly  while  an  attempt  is  made 
to  sound  the  letter  E. 

Aerofoil  Aerofoil  (m)  (ah-ay-roh-foahl)  :  A  winglike  structure,  flat  or 
curved,  designed  to  obtain  reaction  upon  its  surface  from  the  air  through 
which  it  moves. 

Aileron  (Wing  Flap)  Aileron  (m)  (ay-ler-rohng)  :  A  movable  auxiliary  sur- 
face used  to  produce  a  rolling  motion  about  the  fore  and  aft  axis. 

Aircraft  Aeronef  (m)  (ah-ay-roh-neff)  Any  form  of  craft  designed  for  the 
navigation  of  the  air — airplanes,  balloons,  dirigibles,  helicopters,  kites,  kite 
balloons,  ornithopters,  gliders,  etc. 

irp  ane    \  Aeroplane    (m)      (ah-ay-roh-plahn)  :     A   form   of  aircraft   heavier 

than  air  which  has  wing  surfaces  for  support  in  the  air,  with  stabilizing 
surfaces,  rudders  for  steering,  and  power  plant  for  propulsion  through  the 
air.  This  term  is  commonly  used  in  a  more  restricted  sense  to  refer  to 
airplanes  fitted  with  landing  gear  suited  to  operation  from  the  land.  If  the 
landing  gear  is  suited  to  operation  from  the  water,  the  term  "seaplane"  is 
used.  (See  definition.) 

Airplane,  Pusher  Aeroplane  a  helice  arriere  (m)  (ah-ay-roh-plahn  ah  ay-leece 
ah-ree'air)  :  A  type  of  airplane  with  the  propeller  in  the  rear  of  the  wings. 

Airplane,  Tractor  Aeroplane  a  helice  avant  (m)  (ah-ay-roh-plahn  ah  ay-leece 
ah  vohng)  :  A  type  of  airplane  with  the  propeller  in  front  of  the  wings. 

Air-speed  Meter  Metre  a  Vitesse  (m)  (met'trah'vee-tess)  :  An  instrument 
designed  to  measure  the  speed  of  an  aircraft  with  reference  to  the  air. 

Altimeter  Altimetre  (m)  (ahl'tee'met'r)  :  An  aneroid  mounted  on  an  air- 
craft to  indicate  continuously  its  height  above  the  surface  of  the  earth. 

Anemometer  Anemomctre  (m)  (ah-nee-moh-met'r)  :  Any  instrument  for 
measuring  the  velocity  of  the  wind. 

Angle     Angle   (m)      (aunggel)  :     Angle. 

187 


188  Practical    Aviation 


Angle  of  Incidence  Angle  d' incidence  (m)  (aunggel  den-see-daunce)  :  The 
acute  angle  between  the  direction  of  the  relative  wind  and  the  chord  of  an 
aerofoil ;  i.  e.,  the  angle  between  the  chord  of  an  aerofoil  and  its  motion  rela- 
tive to  the  air.  (This  definition  may  be  extended  to  any  body  having  an  axis.) 

Angle,  Critical  Angle  d'at.taqite  (m)  (aunggel  dah'tack)  :  The  angle  of  attack  at 
which  the  lift  curve  has  its  first  maximum ;  sometimes  referred  to  as  the 
"burble  point."  (If  the  "lift  curve"  has  more  than  one  maximum,  this  refers 
to  the  first  one.) 

Angle,  Gliding  Angle  de  descent  e  (m)  (aunggel  der  day'saunt)  :  The  angle 
the  flight  path  makes  with  the  horizontal  when  flying  in  still  air  under  the 
influence  of  gravity  alone,  i.  e.,  without  power  from  the  engine. 

Appendix  Appendix  (m)  (ah-paungdix)  :  The  hose  at  the  bottom  of  a  balloon 
used  for  inflation.  In  the  case  of  a  spherical  balloon  it  also  serves  for 
equalization  of  pressure. 

Aspect  ratio  Allongement  (m)  (ah-longe-maung)  :  The  ratio  of  span  to  chord  of 
an  aerofoil. 

Aviator  Amateur  (m)  (ah-vee'ah-teur)  :  The  operator  or  pilot  of  heavier-than- 
air  craft.  This  term  is  applied  regardless  of  the  sex  of  the  operator. 

Axes  of  an  Aircraft  Essieux  (m)  (ess-seu)  :  Three  fixed  lines  of  reference; 
-  usually  centroidal  and  mutually  rectangular.  The  principal  longitudinal 
axis  in  the  plane  of  symmetry,  usually  parallel  to  the  axis  of  the  propeller,  is 
called  the  fore  and  aft  axis  (or  longitudinal  axis)  ;  the  axis  perpendicular  to 
this  in  the  plane  of  symmetry  is  called  the  vertical  axis ;  and  the  third  axis, 
perpendicular  to  the  other  two,  is  called  the  transverse  axis  (or  lateral  axis). 
In  mathematical  discussions  the  first  of  these  axes,  drawn  from  front  to 
rear,  is  called  the  X  axis ;  the  second,  drawn  upward,  the  Z  axis ;  and  the 
third,  forming  a  "left-handed"  system,  the  Y  axis. 

Ballonet  Ballonnet  (m)  (bah-loh-nay)  :  A  small  balloon  within  the  interior 
of  a  balloon  or  dirigible  for  the  purpose  of  controlling  the  ascent  or  descent, 
and  for  maintaining  pressure  on  the  outer  envelope  so  as  to  prevent  de- 
formation. The  ballonet  is  kept  inflated  with  air  at  the  required  pressure, 
under  the  control  of  a  blower  and  valves. 

Balloon  Ballon  (m)  (bah'lon)  :  A  form  of  aircraft  comprising  a  gas  bag 
and  a  basket.  The  support  in  the  air  results  from  the  buoyancy  of  the  air 
displaced  by  the  gas  bag,  the  form  of  which  is  maintained  by  the  pressure 
of  a  contained  gas  lighter  than  air. 

Balloon,  Barrage  Ballon  barrage  (m)  (bah'lon  bah-rahge)  :  A  small  spherical 
captive  balloon,  raised  as  a  protection  against  attacks  by  airplanes. 

Balloon,  Captive  Ballon  captif  (m)  (bah'lon  cap-tiff)  :  A  balloon  restrained 
from  free  flight  by  means  of  a  cable  attaching  it  to  the  earth. 

Balloon,  Kite  Ballon  d' observation  (m)  (bah'lon  dohps-sair-vah-see'ohn")  :  An 
elongated  form  of  captive  balloon,  fitted  with  tail  appendages  to  keep  it 
headed  into  the  wind,  and  deriving  increased  lift  due  to  its  axis  being  inclined 
to  the  wind. 

Balloon,  Pilot  Ballon  pilote  (m)  (bah'lon  pee-lot)  :  A  small  spherical  balloon 
sent  up  to  show  the  direction  of  the  wind. 

Balloon,  Sounding  Ballon  sonde  (m)  (bah'lon  sohnd)  :  A  small  spherical 
balloon  sent  aloft,  without  passengers,  but  with  registering  meteorological 
instruments. 


Appendix  189 


Balloon  bed  Ballon  terrain  d'atterrissage  (m)  (bah'lon  tay'rahns  dah-tay-ree- 
sahge)  :  A  mooring  place  on  the  ground  for  a  captive  balloon. 

Balloon  cloth  Ballon  tissu  pour  toile  caoutchoutee  (m)  (bah'lon  tee'seu  poor 
twahl  cow-chew-tay)  :  The  cloth,  usually  cotton,  of  which  balloon  fabric? 
are  made. 

Balloon  Fabric:  The  finished  material,  usually  rubberized,  cf  which  balloon 
envelopes  are  made. 

Bank  Gauchir  (v)  (go-sheer)  :  To  incline  an  airplane  laterally — i.  e.,  to  roll 
it  about  the  fore  and  aft  axis.  Right  bank  is  to  incline  the  airplane  with  the 
right  wing  down.  Also  used  as  a  noun  to  describe  the  position  of  an  airplane 
when  its  lateral  axis  is  inclined  to  the  horizontal. 

Barograph  Barograph  (m)  (bah-roh-graph)  :  An  instrument  used  to  record 
variations  in  barometric  pressure.  In  aeronautics  the  charts  on  which  the 
records  are  made  indicate  altitudes  directly  instead  of  barometric  pressures. 

Basket  Nacelle  (f)  (nah'cell)  :  The  car  suspended  beneath  a  balloon,  for 
passengers,  ballast,  etc. 

Biplane  Biplan  (m)  (bee'plohng)  :  A  form  of  airplane  in  which  the  main 
supporting  surface  is  divided  into  two  parts,  one  above  the  other. 

Body  of  an  Airplane  Fuselage  (m)  (feu'zeh-lahge)  :  The  structure  which 
contains  the  power  plant,  fuel,  passengers,  etc. 

Bonnet  Bonnet  (m)  (bohn'ay)  :  The  appliance  having  the  form  of  a  paraso. 
which  protects  the  valve  of  a  spherical  balloon  against  rain. 

Cabane  Cabane  (f)  (kah'bahn)  :  A  pyrmadial  framework  upon  the  wing  of 
an  airplane,  to  which  stays,  etc.,  are  secured. 

Camber  Courbitre  (f)  (keer-beur)  :  The  convexity  or  rise  of  the  curve  of  an 
aerofoil  from  its  chord,  usually  expressed  as  the  ratio  of  the  maximum  de- 
parture of  the  curve  from  the  chord  to  the  length  of  the  chord.  "Top  camber" 
refers  to  the  top  surface  of  an  aerofoil,  and  ''bottom  camber"  to  the  bottom 
surface;  "mean  camber"  is  the  mean  of  these  two. 

Center  Centre  (m)  (saunt'r)  Of  pressure  of  an  aerofoil. — The  point  in  the 
plane  of  the  chords  of  an  aerofoil,  prolonged  if  necessary,  through  which  at 
any  given  attitude  the  line  of  action  of  the  resultant  air  force  passes.  (This 
definition  may  be  extended  to  any  body.) 

Chord  Corde  (f)  (kord)  :  Of  an  aerofoil  section. — A  right  line  tangent  at 
the  front  and  rear  to  the  under  curve  of  an  aerofoil  section. 

Length. — The  length  of  the  chord  is  the  length  of  the  projection  of  the 
aerofoil  section  on  the  chord. 

Clinometer  (inclinometer)  Indicateur  de  pente  (m)  (ahn-dee-kah-teur  der 
paunt)  :  An  instrument  for  measuring  the  angle  made  by  any  axis  of  an  air- 
craft with  the  horizontal,  often  called  an  inclinometer. 

Controls  Commandes  (f)  (koh-maund)  :  A  general  term  applying  to  the 
means  provided  for  operating  the  devices  used  to  control  speed,  direction  of 
flight,  and  attitude  of  an  aircraft. 

Control  column  Levier  de  commande  (m)  (ler  vee'ay  der  koh-maund)  :  The 
vertical  lever  by  means  of  which  certain  of  the  principal  controls  are  operated, 
usually  those  for  pitching  and  rolling. 


190  Practical    Aviation 


Decalage  Longitudinal  V  (m)  (lohng-gee-teu-dee'nahl)  :  The  angle  between 
the  chords  of  the  principal  and  the  tail  planes  of  a  monoplane.  The  same 
term  may  be  applied  to  the  corresponding  angle  between  the  direction  of  the 
chord  or  chords  of  a  biplane  and  the  direction  of  a  tail  plane.  (This  angle  is 
also  sometimes  known  as  the  longitudinal  V  of  the  two  planes.) 

Dihedral  in  an  airplane  Dicdre  (a)  (dee-ay'd'r)  :  The  angle  included  at  the 
intersection  of  the  imaginary  surfaces  containing  the  chords  of  the  right  and 
left  wings  (continued  to  the  plane  of  symmetry  if  necessary).  This  angle 
is  measured  in  a  plane  perpendicular  to  that  intersection.  The  measure  of 
the  dihedral  is  taken  as  90°  minus  one-half  of  this  angle  as  denned.  The 
dihedral  of  the  upper  wing  may  and  frequently  does  differ  from  that  of 
the  lower  wing  in  a  biplane. 

Dirigible  Dirigeable  (m)  (dee-ree-zhah'bl)  :  A  form  of  balloon,  the  outer 
envelope  of  which  is  of  elongated  form,  provided  with  a  propelling  system, 
car,  rudders,  and  stabilizing  surfaces. 

Dirigible,  Nonrigid  Dirigeable  Nonrigide  (m)  (dee-ree-zhah'bl  noh-ree'zghid)  : 
A  dirigible  whose  form  is  maintained  by  the  pressure  of  the  contained  gas 
assisted  by  the  car-suspension  system. 

Dirigible,  Rigid  Dirigeable  Rigide  (m)  (dee-ree-zhah'bl  ree'zghid)  :  A  dirigble 
whose  form  is  maintained  by  a  rigid  structure  contained  within  the  envelope. 

Dirigible,  Semirigid  Dirigeable  Semi-rigide  (m)  (dee-ree-zhah'bl  ser-me-ree- 
zghid)  :  A  dirigible  whose  form  is  maintained  by  means  of  a  rigid  keel 
and  by  gas  pressure. 

Diving  Rudder  (elevator)  Gouvernal  de  Profondeur  (m)  (goo-vair-nahl  dcr 
proh-fohng-dare)  :  A  hinged  surface  for  controlling  the  longitudinal  attitude 
of  an  aircraft ;  i.  e.,  its  rotation  about  the  transverse  axis. 

Dope  Enduire  (v)  (aungdweer)  :  A  general  term  applied  to  the  material 
used  in  treating  the  cloth  surface  of  airplane  members  and  balloons  to 
increase  strength,  produce  tautness,  and  act  as  a  filler  to  maintain  air- 
tightness  ;  it  usually  has  a  cellulose  base. 

Drag  (drift)  Derive  (f)  (day-reeve)  :  The  component  parallel  to  the  rela- 
tive wind  of  the  total  force  on  an  aircraft  due  to  the  air  through  which  it 
moves.  That  part  of  the  drag  due  to  the  wings  is  called  "wing  resistance" 
(formerly  called  "drift")  ;  that  due  to  the  rest  of  the  airplane  is  called  "para- 
site resistance"  (formerly  called  "head  resistance"). 

Drift  (see  Drag)  :     Also  used  as  synonymous  with  "leeway,"  g.  v. 

Drift-meter  Metre  de  la  derive  (m)  (met'r  der  lah  day-reeve)  :  An  instru- 
ment for  the  measurement  of  the  angular  deviation  of  an  aircraft  from  a  set 
course,  due  to  cross  winds. 

Elevator   (see  Diving  Rudder) 

Entering  edge  Bord  d'attaque  (m)  (boar  dah-tack)  :  The  foremost  edge  of 
an  aerofoil  or  propeller  blade. 

Envelope  Envelope  (f)  (envelope)  :  The  portion  of  the  balloon  or  dirigible 
which  contains  the  gas. 

Epannage  (tail)  Queue  (f)  (keu)  :  The  rear  portion  of  an  aircraft,  to 
which  are  usually  attached  rudders,  elevators,  stabilizers,  and  fins. 


Appendix  191 


Equator  Equateur  (m)  (ay-quah-teur)  :  The  largest  horizontal  circle  of  a 
spherical  balloon. 

Float  Flotteur  (m)  (flo'teur)  :  That  portion  of  the  landing  gear  of  an  air- 
craft which  provides  buoyancy  when  it  is  resting  on  the  surface  of  the  water. 

Gap  Espace  (f)  (ess-pass)  :  The  shortest  distance  between  the  planes  of  the 
chords  of  the  upper  and  lower  wings  of  a  biplane. 

Glide     Vol  Plane  (m)     (vol  plah'nay)  :      To  fly  without  engine  power. 

Glider  Flaneur  (m)  (plah'nair)  :  A  form  of  aircraft  similar  to  an  airplane, 
but  without  any  power  plant.  When  utilized  in  variable  winds  it  makes  use 
of  the  soaring  principles  of  flight  and  is  sometimes  called  a  soaring  machine. 

Guide  rope  Cordz  a  guider  (f)  (kord  ah  gid-day)  :  The  long  trailing  rope 
attached  to  a  spherical  balloon  or  dirigible,  to  serve  as  a  brake  and  as  a 
variable  ballast. 

Guy  Hauban  (m)  (oh-baung)  :  A  rope,  chain,  wire,  or  rod  attached  to  an 
object  to  guide  or  steady  it,  such  as  guys  to  wing,  tail,  or  landing  gear. 

Hangar     Hangar  (m)      (aunggahr)  :     A  shed  for  housing  balloons  or  airplanes. 

Helicopter  Helicopterc  (m)  (ay-lee-copt-air)  :  A  form  of  aircraft  whose 
support  in  the  air  is  derived  from  the  vertical  thrust  of  propellers. 

Inclinometer  (see  Clinometer) 

Horn  Guignol  (m)  (ginn-yol)  :  A  short  arm  fastened  to  a  movable  part  of 
an  airplane,  serving  as  a  lever-arm,  e.  g.,  aileron-horn,  rudder-horn,  elevator- 
horn. 

Inspection  window  Porte  de  visite  (f)  (port  der  visit)  :  A  small  transparent 
window  in  the  envelope  of  a  balloon  or  in  the  wing  of  an  airplane  to  allow 
inspection  of  the  interior. 

Kite  C  erf -volant  (m)  (sair-voh-lohng)  :  A  form  of  aircraft  without  other 
propelling  means  than  the  towline  pull,  whose  support  is  derived  from  the 
force  of  the  wind  moving  past  its  surface. 

Landing  gear  Train  d'atterrissage  (m)  (trahns  dah-tay-ree-sahge)  :  The  un- 
derstructure  of  an  aircraft  designed  to  carry  the  load  when  resting  on  or 
running  on  the  surface  of  the  land  or  water. 

Leeway  Derive  due  au  vent  lateral  (f )  (day-reeve  deu  oh  vaung  lah-tay-rahl)  : 
The  angular  deviation  from  a  set  course  over  the  earth,  due  to  cross  cur- 
rents of  wind,  also  called  drift ;  hence,  "drift  meter." 

Lift  Pousse  e  (f)  (poo-say)  :  The  component  perpendicular  to  the  relative 
wind,  in  a  vertical  plane,  of  the  force  on  an  aerofoil  due  to  the  air  pressure 
caused  by  motion  through  the  air. 

Load,  dead  Poids  mort  (m)  (poo'ah  more)  :  The  structure,  power  plant,  and 
essential  accessories  of  an  aircraft. 

Load,  full  Poids  total  (m)  (poo'ah  toh'tahl)  :  The  maximum  weight  which 
an  aircraft  can  support  in  flight ;  the  "gross  weight." 

Load,  useful  Poids  utile  (m)  (poo'ah  eu'teel)  :  The  excess  of  the  full  load 
over  the  dead-weight  of  the  aircraft  itself,  i.  e.,  over  the  weight  of  its  struc- 
ture, power  plant,  and  essential  accessories.  (These  last  must  be  specified.) 


192  Practical    Aviation 


Monoplane  Mono  plan  (m)  (moh-noh-plohng)  :  A  form  of  airplane  whose 
main  supporting  surface  is  a  single  wing,  extending  equally  on  each  side  of 
the  body. 

Net  Filet  (m)  (fee'lay)  :  A  rigging  made  of  ropes  and  twine  on  spherical 
balloons,  which  supports  the  entire  load  carried. 

Ornithopter  Ornithophcre  (m)  (ornee-top-tair)  :  A  form  of  aircraft  deriv- 
ing its  support  and  propelling  force  from  flapping  wings. 

Parachute  Parachute  (m)  (pah-rah-shoot)  :  An  apparatus,  made  like  an  um- 
brella, used  to  retard  the  descent  of  a  falling  body. 

Permeability  Penneabilite  (m)  (pair-may-ah-bee-lee-tay)  :  The  measure  of 
the  loss  of  gas  by  diffusion  through  the  intact  balloon  fabric. 

Pitot  tube  Tube  de  Pilot  (m)  (tueb  der  peet'yoh)  :  A  tube  with  an  end  open 
square  to  the  fluid  stream,  used  as  a  detector  of  an  impact  pressure.  It  is 
usually  associated  with  a  coaxial  tube  surrounding  it,  having  perforations 
normal  to  the  axis  for  indicating  static  pressure ;  or  there  is  such  a  tube 
placed  near  it  and  parallel  to  it,  with  a  closed  conical  end  and  having  per- 
forations in  its  side.  The  velocity  of  the  fluid  can  be  determined  from  the 
difference  between  the  impact  pressure  and  the  static  pressure,  as  read  by 
a  suitable  gauge.  This  instrument  is  often  used  to  determine  the  velocity  of 
an  aircraft  through  the  air. 

Pylon  Pylone  (m)  (pee'lone)  :  A  mast  or  pillar  serving  as  a  marker  of  a 
course. 

Relative  wind  Vent  relatif  (m)  (vaung  ray'lah-tiff)  :  The  motion  of  the  air 
with  reference  to  a  moving  body.  Its  direction  and  velocity,  therefore,  are 
found  by  adding  two  vectors,  one  being  the  velocity  of  the  air  with  reference 
to  the  earth,  the  other  being  equal  and  opposite  to  the  velocity  of  the  body 
with  reference  to  the  earth. 

Rudder  Gouvernail  de  direction  (m)  (goo-vair-nah'ee  der  dee-reck-see-ohng)  : 
A  hinged  or  pivoted  surface,  usually  more  or  less  flat  or  streamlined,  used 
for  the  purpose  of  controlling  the  attitude  of  an  aircraft  about  its  "vertical" 
axis,  i.  e.,  for  controlling  its  lateral  movement. 

Rudder  bar  Palonnier  (m)  (pah-lun'yay)  :  The  foot  bar  by  means  of  which  the 
rudder  is  operated. 

Seaplane  Hydroplane  (m)  (ee-droh-plahn)  :  A  particular  form  of  airplane  in 
which  the  landing  gear  is  suited  to  operation  from  the  water. 

Side  slipping  Glissade  sur  I'aile  (f)  (glee-sahd  seur  Tell)  :  Sliding  downward 
and  inward  when  making  a  turn ;  due  to  excessive  banking.  It  is  the  opposite 
of  skidding. 

Skids  Be^uilles  (f)  (bay-kee'e)  :  Long  wooden  or  metal  runners  designed  to 
prevent  nosing  of  a  land  machine  when  landing  or  to  prevent  dropping  into 
holes  or  ditches  in  rough  ground.  Generally  designed  to  function  should  the 
landing  gear  collapse  or  fail  to  act. 

Slip  stream  (Propeller  race)  Vent  de  I'helice  (m)  (vaung  der  lay-leece)  : 
The  stream  of  air  driven  aft  by  the  propeller  and  with  a  velocity  relative  to 
the  airplane  greater  than  that  of  the  surrounding  body  of  still  air. 

Soaring  machine     Flaneur  (m)      (plah'nair)  :     See  Glider. 


Appendix  193 


Span  (spread)  Envergure  (f)  (aung  vair-geur)  :  The  maximum  distance  lat- 
erally from  tip  to  tip  of  an  airplane  wing,  or  the  lateral  dimension  of  an 
aerofoil. 

Stability  Stabilite  (f)  (stah-bee-lee-tay)  :  A  quality  in  virtue  of  which  an 
airplane  in  flight  tends  to  return  to  its  previous  attitude  after  a  slight  dis- 
turbance. 

Stability,  Directional  Stabilite  en  direction  (f)  (stah-bee-lee-tay  aung  dee-reck- 
see-ohng)  :  Stability  with  reference  to  the  vertical  axis. 

Stability,  Dynamical  Stabilite  dynamique  (f)  (stah-bee-lee-tay  dee-nah-mick)  : 
The  quality  of  an  aircraft  in  flight  which  causes  it  to  return  to  a  condition 
of  equilibrium  after  its  attitude  has  been  changed  by  meeting  some  disturb- 
ance, e.  g.,  a  gust.  This  return  to  equilibrium  is  due  to  two  factors;  first, 
the  inherent  righting  movements  of  the  structure ;  second,  the  damping  of  the 
oscillations  by  the  tail,  etc. 

Stability,  Inherent  Stabilite  inker ente  (f )  (stah-bee-lee-tay  angay-raunt)  Sta- 
bility of  an  aircraft  due  to  the  disposition  and  arrangement  of  its  fixed  parts ; 
i.  e.,  that  property  which  causes  it  to  return  to  its  normal  attitude  of  flight 
without  the  use  of  the  controls. 

Stability,  Lateral  Stabilite  later  ale  (f)  (stah-bee-lee-tay  lah-tay-rahl)  :  Sta- 
bility with  reference  to  the  longitudinal  (or  fore  and  aft)  axis. 

Stability,  Statical  Stabilite  statique  (f)  (stah-bee-lee-tay  staht-tick)  :  In  wind 
tunnel  experiments  it  is  found  that  there  is  a  definite  angle  of  attack  so 
that  for  a  greater  angle  or  a  less  one  the  righting  movements  are  those  which 
tend  to  make  the  attitude  return  to  this  angle.  This  holds  true  for  a 
certain  range  of  angles  on  each  side  of  this  definite  angle ;  and  the  machine 
is  said  to  possess  "statical  stability"  through  this  range. 

Stabilizer  Plan  fixe  de  queue  (m)  (plohng  fix  der  keu)  :  Any  device  designed 
to  steady  the  motion  of  aircraft. 

Stagger  Decalage  des  ailes  (m)  ( day-kah-lahge  dayzail)  :  The  amount  of 
advance  of  the  entering  edge  of  the  upper  wing  of  a  biplane  over  that  of  the 
lower,  expressed  as  percentage  of  gap;  it  is  considered  positive  when  the 
upper  surface  is  forward. 

Stalling  Perte  de  vitesse  (f)  (pert  der  vee'tesse)  :  A  term  describing  the  con- 
dition of  an  airplane  which  from  any  cause  has  lost  the  relative  speed  neces- 
sary for  control. 

Statoscope  Statoscope  (m)  (stah-toh-scup)  :  An  instrument  to  detect  the  ex- 
istence of  a  small  rate  of  ascent  or  descent,  principally  used  in  ballooning. 

Stay  Haubans  (m)  (oh-baung)  :  A  wire,  rope,  or  the  like  used  as  a  tie  piece 
to  hold  parts  together,  or  to  contribute  stiffness;  for  example,  the  stays  of 
the  wing  and  body  trussing. 

Step     Ressaut  (m)      (resso)  :     A  break  in  the  form  of  the  bottom  of  a  float. 

Strut  Montant  (m)  (mohng-taung)  :  A  compression  member  of  a  truss  frame ; 
for  instance,  the  vertical  members  of  the  wing  truss  of  a  biplane. 

Tail      Queue  (f )      (keu)  :     See  Epannage. 

Thimble  Cosse  (f)  (koss)  :  An  elongated  metal  eye  spliced  in  the  end  of  a 
rope  or  cable. 


194 


Practical    Aviation 


Trailing  edge      Bord  de  sortie  (m) 
an  aerofoil  or  propeller  blade. 


(bore  der  sor'tee)  :     The  rearmost  edge  of 


Triplane  Triplan  (m)  (tree-plahng)  :  A  form  of  airplane  whose  main  sup- 
porting surface  is  divided  into  three  parts,  superimposed. 

Truss  P outre  armee  (f)  (poo'trahr-may)  :  The  framing  by  which  the  wing 
loads  are  transmitted  to  the  body ;  comprises  struts,  stays,  and  spars. 

Warp    Gauchir  (v)      (go-sheer)  :  To  change  the  form  of  the  wing  by  twisting  it. 

Wash  out  Reglage  de  I' incidence  (m)  (ray-glahge  der  lence-see-daunce)  :  A 
permanent  warp  of  an  aerofoil  so  that  the  angle  of  attack  decreases  toward 
the  wing  tips. 

Wings     Ailes  (f)      (ale)  :     The  main  supporting  surfaces  of  an  airplane. 
Wing  flap    Aileron   (m)      (ale-ler  rohns)  :     See  Aileron. 

Wing  mast  Mat  (m)  (mah)  :  The  mast  structure  projecting  above  the  wing, 
to  which  the  top  load  wires  are  attached. 

Wing  rib  Nervure  (f)  (ner'veur)  :  A  fore  and  aft  member  of  the  wing 
structure  used  to  support  the  covering  and  to  give  the  wing  section  its  form. 

Wing  spar  (wing  beam)  Longeron  (m)  (lohng-zher-rohng)  :  A  transverse 
member  of  the  wing  structure. 

Yaw  Louvoyer-mouvement  de  lacet  (m)  (loo-vwah-yay  move-maung  der 
lah'say)  :  To  swing  off  the  course  about  the  vertical  axis. 

Angle  0/>^-The  temporary  angular  deviation  of  the  fore-and-aft  axis 
from  the  course. 


METRIC  CONVERSION     TABLES 

1  kilometer  =  0.6214    mile.  1  mile  =  1.609   kilometers. 

1  meter=  3.2808  feet.  1  foot=  0.3048    meter. 

1  centimeter = 0.3937  inch.  1  inch  =  2.54    centimeters. 


1  sq.  meter=  10.764  sq.   feet. 

1  sq.  centimeter  =  0.155   sq.   inch. 

1  cub.   meter=  35.314    cub.    feet. 
1  liter  =  0.0353    cubic   foot. 

1  kilogram  =  2. 2046    pounds. 


1  sq.  foot =0.0929  sq.  meter. 

1  sq.  inch  =  6.452   sq.    centimeters. 

1  cub.  foot  =  28.317   liters. 
1  U.    S.   gallon  =  3.785  liters. 

1  pound  =  0.4536  kilogram. 


RULES    FOR   MENSURATION 

Triangle — Area  equals  one-half  the  product  of  the  base  and  the  altitude. 

Parallelogram — Area  equals  the  product  of  the  base  and  the  altitude. 

Irregular  figure  bounded  by  straight  lines — Divide  the  figure  in  triangles,  and  find  the  area  of  each  triangle 

separately.     The  sum  of  the  areas  of  all  the  triangles  equals  the  area  of  the  figure. 
Circle — Circumference   equals   diameter  multiplied   by   3.1416. 
Circle — Area   equals   diameter   squared,   multiplied   by    0.7854. 
Circular  arc — Length   equals   the  circumference  of  the   circle,  multiplied  by  the  number  of  degrees   in   the 

arc,  divided  by  360. 
Circular   sector — Area  equals   the   area   of   the   whole   circle   multiplied   by   the   quotient   of   the   number   of 

degrees  in  the  arc  of  the  sector  divided  by   360. 
Circular   segment — Area   equals    area   of   circular   sector   formed   by   drawing  radii    from   the   center   of  the 

circle   to   the    extremities    ot    the   arc    of   the   segment,   minus    area   of   triangle    formed    by   the   radii 

and  the  chord  of  the  arc  of  the  segment. 

Prism — Volume  equals  the  area  of  the  base  multiplied  by  the  altitude. 
Cylinder — Volume  equals  the  area  of  the  base  circle  times  the  altitude. 
Pyramid  or  Cone — Volume  equals  the  area  of  the  base  times  one-third  the  altitude. 


INDEX 


A  Page 

Accuracy  and  Volume  of  Fire 152 

Active    Drift    6 

Advanced  Flying   107,  127 

Aerial    Combat    147 

Aerial  Fountain,   Cascade,  Cataract, 

Breakers     141 

Aerial    Gunnery    147 

Aerial  Photography   (see  Photography) 

Aerial    ( Radio)     181 

Aerobatics  and  Night  Flights    127 

Aerofoil,    The     4 

Aerography     137 

Ailerons     3,    27 

Ailerons,    Rigging   the    46 

Air,    Characteristics   of  the    138 

Composition   of   the    4 

Air  Cooling    75 

Air,    Flow    of    7 

Airdromes     113 

Airplane    Design,     Elements    of     13 

Air    Screw    53 

Air   Speed  Meter    100 

Aligning  the  Airplane    44 

Alignment  Errors,  Effect  of 48 

Alternating    Current     179 

Altimeter 97 

Altitudes.    Warfare    159 

Alto-Stratus  and  Altocumulus  Clouds    ....  143 

Aluminum     38 

Ammunition  and  Fire  Correction    153 

Ampere,   Definition   of    179 

Angles  of  Fire,   Effective   155 

Angle  of  Incidence 5,   8 

Verifying   the    45 

Angle  of  Incidence  Indicator 99 

Angles  of  Incidence  in  Flight   18 

Antenna     (Radio) 181 

Anti-Aircraft  Guns  and  Fire 162 

Anti-Cyclone     138 

Anzani   Engine    85 

Apparatus,   Airplane   Radio    181 

Armament,   Heavy  Airplane    161 

Armor  for  Airplanes    161 

Artillery  Fire,   Directing    177,  178 

Ash ;. .  36 

Aspect    Ratio    9 

Assembly  of  Lifting  Surfaces    43 

Atmospheric   Pressure    138 

Attack,    Skill   in    157 

Attacks  on   Balloons    163 

Aviation  Wire  and  Strand 38 

B 

Balloons,  Attacks  on   .  163 

Banking    3,   27 

Banking   Indicator    100 

Bank,    Vertical    131 

Barometer    97 

Barrel    . 131 

Battle  Reconnaissance 172 

Bearing   119 

Bearings,   .Lost    122 

Beaufort    Scale    139 

Bending  Materials    34 

Billows,  Wind    141 

Bombing  Airplane  Types 165 

Bombing  Air   Raids 165 

Bombing  Crews,  Training   165 

Bombs  and  Bombing    147 

Bomb   Dropping 166 

Bombs,   Types   of    168 

Browning  Gun,  The 151 

Bullets,  Types  of 153 

Bumps 141 


Cables  and  Wires,  Control   47 

Camber    4,    8 

Camera  and  Its  Parts,  The 184 

Cams    66 

Camshaft 66 

Canard   Principle    25 

Carburetion  and  Carburetors    68 

Care   of   Engines    76 

Cavaro    37 

Cedar     36 

Cellon    37 

Center  of   Gravity    22 


Page 

Chord,    The 5 

Circuit    Breaker    74 

Circuit    (Radio)  : 

Closed    181 

Radiating    181 

Cirrus  Family  of  Clouds 143 

Clerget    Engine    85 

Climb,  Angle  of  Best 18 

Climb,  Design  for  Maximum 16 

Climbing     m 

Clinometer    99 

Clock    System   of    Signaling 178 

Closed  Circuit   (Radio)    181 

Clothing,    Aviator's     95 

Clouds,  Classification  of    46- 143 

Clouds,  Fogs  and   Storms,  Avoiding    122 

Cockpit  Arrangement   96 

Code,  General  Service,  International, 

Continental 174 

Code  Signals  for  Artillery  Control   177 

Code  Telegraphing,   Instruction  in    175 

Combat,   Aerial    147 

Combat  Rules    157 

Combustion  Chamber   55 

Compass,   The 97 

Compass,  Use  of  and  Adjustment 117 

Compression   Stroke   56 

Concentration,    Theory    of    159 

Condenser,  Motor  Ignition    •    74 

Radio    181 

Connecting  Rod    55,  64 

Conservation,    Fuel    87 

Contact   Patrol    161 

Continental   Code    174 

Contour     119 

Control,  Stick  and  Dep 29 

Conventional  Map  Signs   118 

Cooling,  Water  and  Air 75 

Cord,  Tinned  Aviator 38 

Correction  of  Machine  Gun  Fire 153 

Copper    38 

Course,  Laying  off  a   121 

Courses,  Flying 104 

Cranking  the  Engine   ... 86 

Crank  Shaft « 55 

Crank  Shaft  and  Crank  Case 65 

Crew,    The   Flying    109 

The    Repair    110 

Crews,   Training  Bombing    165 

Cross-Country   Flight    103,  115 

Crystallization  and  Fatigue   38 

Cumulus   Clouds 143 

Curtiss   Engine 81 

Current,  A.  C.  and  D.  C 179 

Cyclone   138 

Cylinder,   Gasoline  Engine    55 


Datum     ; 119 

Defects,  Cause  of  Flight 48 

Dep  Control  29 

Depressions,  Secondary  139 

Design,  Elements  of  Airplane 13 

Diaphragm  Openings,  Camera  184 

Dihedral,  Main  Surface 25 

Dihedral  Angle,  Longitudinal 24 

Securing  the  45 

Direct  Current 179 

Directional  Stability  21 

Distributor 74 

Dives,  Nose  129 

Dope  , 37 

Drift,  Calculating  Wind  121 

Lift  and 6 

Drift  Meter  100 

Droop  46 

Dual  Control  Instruction  105 

Dynamo,  D.  C.  and  A.  C.  . . . 179,  181 


Eddies,  Vertical  Wind 141 

Eight-Cylinder  Motor 81 

Elasticity  of  Air 4 

Elevator,   The    3 

Elevators,   Rigging  of    42 

Emaillite    • 37 

Engineer,  The  Motor 109 

Engines,   Multiple   Cylinder 58 

Equipment   for   Night   Flying    133 


195 


Page 

Equivalent,    Horizontal    15 

Erection   and  Assembly   42 

Estimates  of  Enemy  Strength    172 

Exciter,    Radio    181 

Exhaust  Stroke 56 

Expanding  Bullets    153 

Explosive  Machine  Gun  Bullets   153 


Factor  of  Safety 33 

Factor,  to  Determine  Wind 121 

Fatigue,  Crystallization  and 38 

Ferrules,   Metal  for    38 

Field  Resistance   (Radio)    181 

Films  and  Plates,  Camera    184 

Finder,  Camera 184 

Fire,  Accuracy  and  Volume  of    . ..  152 

Correction  of  Machine  Gun    153 

Directing  Artillery    177,  178 

Effective  Angles  of 155 

Spotting    171 

Firing  Order  of  Engines 58,  59 

Flaps,  Wing 3,   27 

Flares    165 

Flat   Turn    132 

Fleet,  Employment  of  the  Air 159 

Flight,  Theory  and  Principles  of 1 

Float-Offs     Ill 

Flow   of   Air    7 

Flying,  Instruction  in   103 

Forced    Landings    123 

Force-Feed  Lubrication    76 

Formation,    Flying    in     158 

Four-Cycle   Principle    56 

Four-Cylinder  Operation    : 58 

Fuselage,   The    3 


Gauges    96 

General   Service   Code 174 

Generating  Electrical  Power  (Radio)    181 

Generator,    Radio    181 

Gnome    Engine    85 

Goggles,    Aviator's    95 

Gradient    119 

Grass-€utter    107 

Gravity,   Center  of 22 

Grip,   Proper  Telegraphing   175 

Ground,    Radio  Apparatus    181 

Ground,   Signals  From  the   178 

Ground  Targets   152 

Gunner,  The   109 

Gunnery,   Aerial    147 

Gusts,    Wind    141 

H 

Hachures    119 

Head  Resistance   7 

Helicopter,    The    1 

Helpers,   Mechanician    110 

Hickory    36 

Horizontal  Equivalent   15 

Horizontal  Stabilizer,   Rigging  of    42 


Ignition,  Cooling  and  Lubrication   73 

Immelman  Turn    132 

Incendiary  Bombs  .  ., 168 

Incidence,   Angle  of    5 

Inclinometer    99 

Indicators    99,  100 

Inertia,  Air 4 

Information,  Gathering   172 

Instability,  Causes  of 48 

Instruments  and  Equipment  for  Flight   ....      94 

Intake   Stroke    56 

International    Code    174 


Joy    Stick 29 

Junior  Military  Aviator  Tests    104 

K 

Key.    Radiotelegraph    181 

Kilowatt,   Definition  of 179 

Knocking,  Engine   92 

L 

Landing  at  Night 134 

(Landing  Gear,  Assembly  of 42 

Landing   Sites    113 

Landings    114 

Forced    123 


Page 

Landmarks     122 

Lateral  Stability    21,   26 

Layers,  Wind 141 

Leaving  the  Ground Ill 

Lens,    Camera    184 

Le  Rhone  Engine   /  85 

Lewis  Machine  Gun,  The 151 

Liberty   Motor,   The    82 

Lift  and  Drift 6 

Lift-Drift   Ratio    7 

Lifting  Surfaces,  Assembly  of   43 

Lighting  the  Field  at  Night 134 

Line   Squalls    139 

Longitudinal  Stability 21,  23 

Loop  the  Loop 130 

Loop,    Spiral    132 

Loops,  Wire 47 

•Lubrication  of  Engines    76 

Luminous  Dials 96 

M 

Machine  Gun,  The  Lewis 151 

Magneto    74 

Magneto    Timing     73 

Mahogany    36 

Maple    36 

Map  Reading 119 

Map,   Weather 139 

Mapping  From  Photographs   184 

Materials,  Stresses  and  Strains   33 

Mechanician,    Aviation     110 

Meridian    119 

Metal  Fittings  and  Wire 38 

Meteorology  for  the  Airman    137 

Meters    100 

Military  Aviator  Flying  Course 106 

Minimum   Angle    18 

Missing.    Engine    90 

Monel   Metal    38 

Monoplane,    The    3 

Motive  Power,  Fundamentals  of 51 

Motor  Engineer 109 

Motors,  Types,  Operation  and  Care 76 

Mountings,   Machine  Gun    155 

Mufflers     165 

N 

Nacelle,    The    3 

Navigator,   The    109 

Night   Flights    127 

Night   Flying   133 

Nimbus   Clouds    143 

Nose  Dive   129 

Novavia     37 

N-Square  Law    159 


Observer,   The    109 

Observer's  Maps  for  Fire  Spotting 177 

Operation  of  Engines 76 

Operator,  The  Radio   109 

Optimum  Angle    18 

Orders  for  Flights   172 

Orienting  a  Map 119 

Ornithopter,  The 1 

Oscillation  Transformer    (Radio)     181 


Pancake,  The   114 

Passive  Drift 6 

Pegging  Down   124 

Penguin     107 

Perforating   Bullets    153 

Photographic  Flights    184 

Photographs,  Mapping  From    184 

Phvsical  Fitness   115 

Pilot,   The    109 

Pine,  Hard   36 

Piston    55 

Piston   Rings    64 

Pistons,   Valves   and   Carburetors    63 

Pitching    3 

Plates  and  Films,   Camera    184 

Power,  Fundamentals  of  Motive 51 

Stroke   56 

Preparations  for  Reconnaissance  Flights   .  .  .  172 

Preparatory  Reconnaissance 173 

Pressure  and  Suction,  Lift  by  Air 5 

Pressure  Areas    . 138 

Primary   of  Transformer    (Radio)     181 

Principles  of  Flight,  Theory  and 1 

196 


Page 

Propeller    53 

Propeller,    Swinging   the    86 

Protective    Reconnaissance    172 

Pusher  Airplane    2 


Quenched  Spark  Gap   (Radio)    181 

Quiz,   Review  : 

Aerial     Gunnery     and     Combat — Bombs 

and  Bombing 169 

Aerobatics   and   Night  Flights    135 

Elements  of  Airplane  Design    19 

First  Flights  and  Cross-Country  Flights  125 

Flight   Stability  and   Control 30 

Fundamentals  of  Motive  Power 61 

Ignition,    Cooling    and    Lubrication    of 

Engines     , 77 

Instruments   and   Equipment   for   Flight  101 

Materials,   Stresses  and   Strains    39 

Meteorology   for  the  Airman    145 

Pistons,  Valves  and  Carburetors   71 

Reconnaissance  and  Fire  Spotting   ....  185 

Rigging  the  Airplane 49 

Theory   and   Principles   of   Flight 11 

Types    of    Motors,    Operation    and    Care 

of  Engines    93 


Radiated  Wave   (Radio)    181 

Radiating  Circuit    (Radio)    181 

Radiator  Temperature  Indicator   99 

Hadio  Apparatus,  Airplane 181 

Radio  Operator,   The   109 

Radio    Receivers    179 

Radiotelegraphy,  Theory  of   179 

Radius  of  Action    122 

Range  Finders  fo.r  Bombing   166 

Ranging,    Artillery    177 

Ratio,  Aspect   9 

Rudder,    Rigging  of    42 

Reaction,    Air    6 

Receivers,    Radio     179 

Receiving  Code    175 

Reconnaissance  and  Fire   Spotting   171 

Reconnaissance  by  Airplane 172 

Repair  Crew,  The 110 

Reports  of  Flights    173 

Resistance  Coil    (Radio)    181 

Re-Starting     124 

Review,    Quiz    (see   Quiz) 

Revolution,  An  Engine 55 

Rigging  the  Airplane 41 

Right  of  Way  in  the  Air .  113 

Rolling 

Roll  Over   131 

Rotary  Engines   !.!!!!  85 

s 

Safety    Belt     95 

Safety,  Factor  of   

Scale,   Beaufort '  139 

Scale,  The  Map .'.'.'.'.'.'.  119 

Screw,    Air    53 

Secondary   Depressions    139 

Secondary  of  Transformer  (Radio)    .               '  181 

Self  Starters    87 

Sending  Code    .'....!    '.  175 

Shearing   34 

Shells,    Artillery    j  *']      \  177 

Signals,   Code  for  Artillery  Control    .......  177 

Signals  From  the  Ground "  178 

Six-Cylinder   Operation    ....  59 

Skid,  The   '  139 

Skin    Friction    .'.I.'."."!.'!.'  6 

Skipping,    Engine    90 

Solo  Method  of  Flying   [  106 

Span    5 

Spark  Gap   (Radio)    '  isi 

Spark    Plug    74 

Speed,  Design  for  Maximum '.'.'.',  17 

Speed  Meter,  Air 100 

Spinning  Nose  Dive   ' '  '  '  109 

Spiral ;  129 

Spiral   Loop    132 

Splash    Lubrication [ .  76 

Spruce \  36 

Squalls,  Line   139 

Stability  and  Control,  Flight 21 

Stabilizers,  Rigging  of 42 

Stagger   10 

Stagger,   To    131 

Start  of  Flight,  The   Ill 


Page 

Starting,  Re-    124 

Starting  the  Engine    86 

Steel    38 

Steering  Direction,  Determining  the '  121 

Stick,    Joy    29 

Stops,   Camera    184 

Straightening   Out    112 

Strategical  Reconnaissance    173 

Strategy    149 

Strato-Cumulus   Clouds    143 

Strength,  Estimates  of  Enemy   172 

Stresses   and   Strains    33 

S-Turns     112 

Surface,   The    4 

Swinging  the  Compass    117 

Swinging  the  Propeller   86 


Tachometer    97 

Tactical    Reconnaissance    .  .  .  172 

Tactical    Skill    159 

Take-Offs    m 

Taking-Off  and  Flying  at  Night    134 

Tanks,   Metal   for    38 

Targets,  Firing  at  Ground   152 

Taxying    m 

Telegraph  Key,   Radio 181 

Tests,    Aviator    , 104 

Theory  and  Principles  of  Flight 1 

Theory  of  Concentration   159 

Thrust,    The    2 

Time   Checking    124 

Timing,   Valve  and   Magneto    73 

Tin 38 

Tinned   Aviator   Cord    38 

Titanine 37 

Tool   Chest,   Airplane    115 

Torrents,  Aerial    141 

Torsion    34 

Tracing    Bullets     153 

Tractor  Airplane 2 

Tran.sfo.rmer  (Radio)    .  .< 181 

Triplane,   The    2 

Trouble  Chart,  Engine 89 

Turn,   Flat    132 

Turnbuckles    47 

Turning 112 

Twelve-Cylinder  Motor    81 

u 

Undercarriage,  Assembly  of   42 

Upside  Down  Flying    13Q 


Valve   Timing    73 

Valves,   Engine 66,  67 

Velocity     7 

Velocity,   Design  for  Maximum    17 

Vertical  Bank    131 

Vertical  Stabilizer,  Rigging  of 42 

Vertical  Wind   Eddies 141 

V-Formation,   Flight  in .  158 

Viscosity  of  Air 4 

Visual    Signaling    175 

Volt,  Definition  of   179 

Volume  of  Fire,  Accuracy  and    152 

V-Type  Motors    81 

w 

Walnut    3fi 

Warfare   Altitudes    

Warping    j.  . 

Washin    

Washout   

Water  Cooling 

Wave  Length   (Radio)    

Weather  Map   

Wedge,  The    [ 

Wind  Factor,  Diagram  to  Determine 

Wing   Covering    

"Wing  Flaps   '.".'.'.'.  .'.3. 

Wire  for  Airplanes   : . 

Wire,  Metal  Fittings  and   

Wireless  Apparatus,   Airplane    

Wireless   Telegraphy,  Theory   of    

Wires,  Control  Cables  and 

Wood,   Strength  of   

Woods  for  Airplanes    

Wrist  Pin  . 


159 
3 

27 
27 
75 
181 
139 
139 
121 
37 
27 
38 
38 
181 
179 
47 
35 
36 
64 


Zooming  131 


197 


Marconi  Institute  Series 
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